I'm a vergin girl never had sex till today. Recently I met with my boyfriend and started having sex but when I do oral his **** become hard but when he started inserting his **** in my vagina his ***** loose its strength and result we can't make sex.
What to do

He might be afraid of having sex with you for all sorts of reasons - he will hurt you, you will insist on marriage, he was brought up to wait until marriage, he will get you pregnant, you have a very resistant hymen, there are many more. Sex often does need communication, so just talk for quite a while, about anything, while lying next to each other and touching, and don't try to have sex until it feels right for him.

Rohit, may I ask how old you both are and if he is/was a virgin too?

Talk with him about what is happening when you aren't in the bedroom. This is a discussion that needs to have as few distractions as possible.

Ask him how much he masturbates. One common issue for men is that they can become accustomed to the feel of their hands and a vagina feels different. It is an issue that can have a fairly easy 'fix'. All he has to do is refrain from masturbating (or use a lighter grip) for few days couple of weeks.

Another common problem is getting distracted especially when changing position. It could be by thoughts of hurting you, getting in the best position or even what happened at work. Experience will help with that problem.

Are you using a hormonal contraceptive such as 'the pill' or are you relying on condoms? Some men lose sensitivity when using a condom and it causes them to lose their erections. You might try a different type that allows for more sensation. Do not have sex without using some type (preferably two) of protection.

Are you ready for sex? Are you aroused enough to be physically ready for sex? Could your reaction to possible pain and the unknown be causing you to tense up or to give off an impression that it isn't what you want?

Has he put his penis even part way into your vagina? I ask because if he has then technically you are both no longer virgins. While some outdated/traditional views say that the breaking of the hymen is when virginity is 'lost', that is not quite correct with modern knowledge. We now know that hymens are not all the same. Some are thinner. Some are thicker. Some are non-existent.