Your cervix is more sensitive during pregnancy, and the light bleeding after sex may have just been from having sex. If you're not cramping or bleeding heavily and passing clots, I'd say you're ok. Just in case you should mention it to your doctor. It's better safe than sorry.
To be honest there really isn't a definitive answer to give you. Some women have experienced your symptoms and gone on to have perfectly nromal pregnancies while others have eventually miscarried either naturall or requiring a d & c. Unfortunately the only thing that is going to give you the answer and peace of mind you are seeking is time. How far along should you be? Is your doctor planning to recheck your HCG levels in a few days?