Sex Q&A: How to Make Sex Less Difficult?
Rather than looking for a short-term fix, you should seek out the root of his problem. He should ask his doctor to refer him to a urologist for a consultation. In the meantime, it's best to stop doing positions that bring you discomfort, and use lots of lubrication to help. He may want to try penetrating you from behind very gently so that he's in control and can angle his penis in a way that won't be painful to either of you.
Nestpert Dr. Pam Spurr, author of Make Love All Night & Talk to Him in the Morning and Naughty Tricks and Sexy Tips: A Couple's Guide to Uninhibited Sexual Pleasure