In my opinion, you don't necessarily need more; you could, or your doctor may want to try something different. I would agree that you should go talk with your prescribing doctor to discuss dosage or a switch. I am going in a couple of weeks to discuss this with my doctor. Meds can be a little tricky; they affect us all a little differently..keep us posted!
With stress in your life, 20 mg of celexa is not enough. It is not wearing off but you apparently need more. Ask your doctor to give you 30 mg and then after 2-3 weeks 40 mg. Then within a month you will know if it works for you.
Call your prescribing doctor about this. It is normally about 6-8 weeks that your doctor wants to see you to find out if the dosage is working for you. If not, it is at this point they normally increase the dosage. This is typical, they always start us out on a low dosage and go from there. This is completely normal, so call your doctor and get some relief. Take care.