What can i do. i am constantly worried im pregnant. im a virgin. had 2 periods since i swam with a guy, i feel stream underwater, worried it was sperm?

You know, but: Your description shows that your knowledge is not able to defeat your irrational emotions that lead to delusional thoughts. Don't underestimate the benefits of your intelligence - it will help you in therapy to strengthen logic against those intrusive ideas. But you need therapy and probably some medication for help. Try not to worry about pregnancy. Do a test, have an exam. Trust results. Best!