Thanks for using health care magic for posting your query.
I have gone through your given history in detail.
In your description yo have mentioned that you have not had sex until you are 24 years and recently you have started having sex.
The most common cause for not able to perform sex is "pressure for performance". This makes things difficult. You should see a psychiatrist
or a sexologist
who can talk to your and discuss about your thoughts about sex.
Secondly for a few days try avoiding masturbation
. Not intending to say that it is harmful, but it will reduce your sexual intent.
If you have problem with your girlfriend try asking her to visit a sexologist with you.
Hope I am able to answer your concerns.
If you have any further query, I would be glad to help you.
In future if you wish to contact me directly, you can use the below mentioned link:
Wish you good health,
Dr. Srikanth Reddy M.D.