Taking more of any medication than as prescribed can lead to harm. Were you prescribed this medication? I ask, because one of the potential issues with taking it, even as prescribed, is interference with medication used to treat high blood pressure. https://www.rxlist.com/cialis-side-effects-drug-center.htm
Please don't take extra - if it's not working for you, you may need to switch medications. Taking more does not increase the likelihood that it will work. It only increases the risk of side effects. https://www.drugs.com/medical-answers/cialis-40mg-extreme-ed-691790/
There is evidence (google scholar if you want to read the papers) that non responders to PDE-5 inhibitors (I am using terms you can search with directly rather than a brand name) had nitric oxide production and endothelial response issues. The production problem can be as simple as adding arginine (I prefer other amino acids because they are not subject to the arginine paradox which occurs when all that arginine appears in the blood all at once) in a pill to the Cialis. There is direct evidence for Cialis with arginine and propionyl carnitine as a treatment for non responders so there is more to this than meets the eye. That more includes, at least, as a component, homocysteine. Homocysteine is a lethal inhibitor of arginase (so that particular instance of the enzyme is never going to work again but you have other instances which is why as homocysteine goes up nitric oxide production goes down) and it makes endothelium less responsive to nitric oxide and the problem gets worse as the level of homocysteine stays high for longer periods of time. The carnitine has the effect of improving the response to nitric oxide and it helps in other ways (just don't think it will make you lean, that is true only if the reason you have excess body fat is a deficiency in the carnitine shuttle) like fatty acid metabolism in the heart in congestive heart failure when combined with CoQ10 so it isn't a waste of money. Supplements are neither the panacea that stores make them out to be or the devils physicians (in my experience, not at all well informed as to what a particular supplement does in pharmacological dosages vs drop in the bucket dosages) believe them to be. The truth, like most things, is somewhere in between. You could eat a lot of watermelon and get the citrulline that your body will make into arginine but whatever you think is "a lot", it isn't. The amount is in the multiple kilo range just to get a couple hundred milligrams; I take 5 grams per day just for my health! Carnitine? found most abundantly in red meat; however, just as with creatine, the amount required would be unhealthy in the extreme whereas creatine even has antidepressant properties and carnitine is good for your heart. What I am saying is that after all the work you have put into improving your diet (more magnesium and potassium and less sodium at the very least, lots more fiber and lots more unsaturated fats) it seems foolish to throw it away by eating a pound of red meat a day. I doubt your prolactin or testosterone are that far off the mark since you have the desire and the function was present previously but it would not hurt to get all that checked as well as a high sensitivity estrogen panel. In regards to that last, the standard lab tests are useful for women and no, you will not get "a ball park figure and see if we need to check further" the test is simply not valid for use in men, you are looking for something closer to 1/100th what a woman would have in her reproductive years. Google will get you TNation (good source with references to check but not a professional forum by any means; still, gyms are filled with lab rats) and scholar will get you papers on clinical chemistry. My caution to you would be this: "we don't know so there is no evidence it will work" is the same --just on the opposite side of a line-- as "we don't know so there is no evidence that it won't work" so be like a carpenter, measure twice and cut once --measure more if you want but not less. I would also add that nothing is without risks or interactions; your body needs arginine under some conditions but it does make some on its own and generally, that is enough. Throw in a blood pressure pill (some of which would make you a non responder to Cialis all by themselves) and now, anything that lowers your blood pressure (as getting rid of that homocysteine would) has the potential to seriously complicate matters. You absolutely want to get rid of the homocysteine excess and prolactin is something that too much or too little, both, carry significant problems for your penis (yeah, there are problems elsewhere but I think any guy would agree, penis first!) to say nothing of the procoagulant effects of estrogen (sorry ladies, it isn't benign even in your body and you have, to paraphrase Bernadette from The Big Bang Theory, had a lifetime riding the dragon, a man's body can't really deal with much more than 25 pg/dl and at the op's age, even 22 would be outside the range) or the BPH like symptoms or unwelcome flaccidity it brings. The point is that I hope you have a physician that will work with you rather than reject anything other than the orthodoxy that he already believes. Sure, sometimes, people have stupid ideas and some stupid ideas keep popping back up decade after decade but this is not laetrile or tape worms in a capsule, this is a very healthy and sex positive couple that wants to keep loving each other every day. I invest a lot of time and money on my health because I want to be like this AlfieWiaa when I get to be 77. Although, I am a long way from there, I find strength and encouragement in his experience. If I might be allowed a bit of crudeness, the next time you grab her hips and penetrate her vagina, take her to pound town and somewhere along the way, give her a good swat on each cheek and a few extra thrusts for me and I will do the same over here to my 50 year old! Bravo Zulu!
Incidentally, and my tongue just jumped out of my mouth for even thinking this, even for sex, more is not always better. There are real risks with blood pressure control and blood staying in places longer than it is supposed to and that is before talking about delivering oxygen to the heart. Go through all your meds (interaction checkers at Epocrates and Drugs.com are reliable --Epocrates is probably what your pharmacy uses-- do both anyway) and check for interactions and side effects. It may not state it directly but something like interferes with smooth muscle relaxation is a problem, erections happen when arteries relax and that happens when smooth muscle relaxes.
I have taken 2x20 mg with no bad effects.
There can be major issues such as a painful or prolonged erection lasting 4 or more hours, besides sudden vision reduction or loss of hearing including dizziness. I would suggest not to go over 20mg, it can be harmful in the context of your age.