Because as any other problem, sexual anxiety has its cause.
Well, usually, these issues can be easily solved by having an open conversation with your partner. Once you explain to them what is worrying you everything will be easier. However, if this does not solve your problem, then the best option is the therapy.
However, there are also some minor things you can do that will help you on your way. Exercising for example is very good. Also, try to make the sex more romantic. Distract yourself, simply said!
Turn on some music, light the candles. Do whatever it takes to improve your sex life. You deserve to have one! A great sex life full of pleasure. Remember that!
You should enjoy sex and not feel anxiety. So, go ahead and start speaking about your issue. Do not suffer on your own. You are not helping anyone.
Who will help me?
Only doctor can really help you solve these mental issues.
Well, if your sexual anxiety is caused by psychological factor. There is no magic pill, no aphrodisiac, no nothing that would help you with this. Therapy is the answer.
You need to learn to talk about your issue. And realize that this issue can be solved.