Young and slim guy with weak erection problems seeking advice

Hi all,
I'm 25 years old, seeking advice to a problem that's been plaguing me for several years now - weak erections. I'm not sure when the problem started because I didn't realize it was a problem at first. Once I did, I slowly started to become more keen on finding a solution. I'll try to organize my thoughts in a digestible way and will be so gracious to any advice I can get.

The problem - I can get (weak) erections during sex or masturbation. I don't really get hard at all otherwise - not at night or in the morning or throughout the day. When I do get one, it's hard enough to penetrate in missionary, but certainly not a full erection. I've noticed that my corpora cavernosa (top) gets reasonably hard and the corpus spongiosum (bottom) and glans (glands) are totally soft. The hardness tends to go away easily. If I flex my PC muscle, I can get the glans (glands) slightly hard during the flex. My erection is never higher than horizontal. Aside, my testicles often hang very low (not sure if that's relevant). I feel it's also important to point out that I have a weak-ish urine stream.

Weight - I am a normal weight (150-160 lbs.) for my height (5'9"). I'm very lean and a little bit muscular. I've always been on the thin side.

Diet - My diet was poor when I was younger. I ate a lot of McDonalds and beef jerky and drank a lot of soda, etc. In recent years, I have made conscious efforts to rectify this. I eat more fruits and nuts. I actually enjoy vegatables now (which I rarely ate before). The same goes for milk, which I lately have been able to drink without strawberry/chocolate sugary goodness. I drink a lot more water now and am generally more conscious about what I put in my body. Admittedly, I have a lot of room to go as I still eat the frequent cheeseburger and french fries.

Drugs/alcohol - I've never smoked or taken any drugs at all. Drinking alcohol is a very rare activity that I've only begun to do in the past couple years, infrequently and in moderation. When I drink, it's possible that my erections are harder but I have no solid evidence on that.

Exercise - In my youth, I was never very active. In the last 5 years I have gradually worked my way up to exercising 3 days/week average. The average work-out is a mixed hour of lifting weights and running.

Diagnosis - I saw a few different doctors (years ago now as I no longer have insurance). The results:

Cholesterol test - I can't remember the exact results, but they were low - somewhere between 100-150. The doctors I've talked to act like that's great, but there is a condition known as Hypocholesterolemia which they apparently are unaware of.

Cardiologist - I have an irregular heartbeat which I understand is the result of a murmur(?). I admit that I don't know much about what's going on here. If I recall correctly, my blood pressure is usually 120/80 when I test at the drug store machine.

Visit with Urologist - He acted like I was crazy and had me take a diabetes test, which came back fine.

Visits with new PCP - She was the most helpful and truly was looking for a resolution. She ordered a couple tests for which the results were supposedly normal, prescribed me a dozen viagra to try out, and referred me to a psychologist specializing in sexual problems.

Visits with psychologist - Although it was fun/interesting talking about sex and my body with a total stranger, this is not what I needed. I think by now I can tell the difference between a physical problem and a mental problem manifesting itself as physical.

Herbs/pills - Since I identified I had a problem in 2003, I have experimented with 1-2 dozen different "supplements". Mostly all of them have an effect of some kind. Occasioanlly, they don't. The urologist I met with told me they're worthless and that they don't do anything. He definitely was mis-informed. Although I try to not make a habit out of taking those, it feels great to get an erection that feels more "normal". I also took a few Cialis pills of my uncle's and that felt the best, better than the Viagra. After taking that, I know what feeling I'm striving to achieve.

I'm here to find out what further steps I can take. Should I completely cut soda and burgers out of my diet? Should I exercise more frequently? There are overweight guys who eat terribly and never exercise that get erections just fine. Should I try to get tested again for cholesterol, diabetes? Should I get some new tests like anemia or thyroid? I'd need these tests/screenings to be cheap or free. I'm desperate for advice. I'm uninsured. I'm willing to do whatever I have to in order to get some help.