It sounds really strange!
For myself and for most people, it is the case that, if having not had sex for a long time, then at the first time back to sex, it would be more difficult to control the ejaculation compared with having sex regularly or just having had sex not too long before.
I have no trouble to last over 20 - 30 minutes during sex. Try to do more kegels; and when masturbation, don’t cum very quickly, and learn how to control your urge. There is a thread talking about the multi-orgasm. Take a look and you will surly benefit. After reading and learning from that thread, now I can have at least 3 times normally 4 or 5 times orgasm during one masturbation session.