I am a 34 year old man - sexually active with a first steady partner and having issues in staying erect for intercourse.

There are 2 topics on which I am looking for suggestions-
(1) Do you think I may have medical problem and see a doctor?
(2) If this is not medical, what can I do to improve?

Little more background:
I always thought the girl I would sleep with I will end up marrying - a belief that quite doesn't fit in today's world. And I don't believe it anymore either.

The first girl I ever dated was at 32, I was a virgin. I should have told her about my virginity to begin with But I didn't as I was afraid of losing her. I was in love. Anyway she dumped me when she found that I wasn't good at sex. At that point I decided not to clarify things that I had been hiding. And she didn't take time to figure out either. Moving on...

I masturbate about 4-5 times/ week. During hand masturbation, I can stay hard and go as long as 10-12 min w/o ejaculation.

Now, 2 years later, I am seeing a new girl. She is more patient with me. We have had sex for 4-6 times. But with the exception of 1st time, I have had issues staying erect for intercourse. Also I am uncircumcised and the head of the penis is very sensitive to an extent that I loose erection if she touches the head of the penis. I am not sure if this is psychological vs. lack of experience vs. health issue. Any tips/ pointers will be helpful.