My penis shrinks before I penetrate. What to do?

Hi doctor,

I am 29 years old, and my partner is 22 years old. We started our life with unpleasant moments after marriage. After a year, we started our sexual life. We are trying for a baby for the past few months. I have a habit of masturbating regularly. Recently, my sperm count and motility got reduced entirely. I consulted a doctor, and the doctor gave me Popson tablets for increasing the sperm count.

Also, my doctor did all the necessary scans for my prostate, and the results came normal. But I am unable to do intercourse properly, and my penis becomes small automatically after a few minutes of trying for insertion. I have irritation in penis and pain during urination. We are not doing any foreplay before sex as my partner is not interested in it. I am very much stressed and depressed. What can I do for my erection problem? Can taking tablets for erection become an addiction? Can I have any side effects? Please help me.