It all depends on where in your cycle you were when you had sex and started bleeding. The bleeding could just be from the sex itself, you may have gotten a scratch or tear inside that is bleeding, you could be starting your period early or you could be experiencing implantation bleeding. If it is implantation bleeding it may be bright pink or dark brown and only enough to be considered 'spotting' and not a period. If it is heavy bleeding it is not implantation bleeding. You can take a test in 1.5 to 2 weeks. Good Luck!
theres a possibility of muscle cramps
If your bleeding is that light you shouldn't be using tampons at all, it's unsafe. You wouldn't menstruate while pregnant, you may see spotting as a result of implantation bleeding but it's ore likely if you're bleeding when due your period it's likely your period. If unsure take a pregnancy test.
I believe the two are unrelated. Whenever pain is envolved, you should seriously consider seeing a doctor.
Unsafe
DO NOT DO THIS!!! UNSAFE!!!!!!!!!! UNSAFE!!!!!!!!!!!! UNSAFE!!!!!!!!!!!!!!
NO, NO, NO, NO, NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! DANGER, DANGER, DANGER, DANGER!!!!!!!!!!!!!!!!!!!!!!! UNSAFE, UNSAFE, UNSAFE, UNSAFE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Unsafe product
DO NOT ATTEMPT TO DO THIS!!!!!!!!!!!!!!!!!!!!!!!!!!!! DANGER, DANGER, DANGER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! UNSAFE, UNSAFE, UNSAFE, UNSAFE
Doing dangerous things will make you unsafe. Inspectors found unsafe conditions in the company's factory.
GET IT TO A GUNSMITH NOW OR SEND IT TO BROWNING!!!!!!!!!!!!! UNSAFE!!!!!!!!!!!!! UNSAFE!!!!!!!!!!!!!!!! UNSAFE!!!!!!!!!!!!!!!!! UNSAFE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
You can be pregnant even if you are having your period. This is especially true if your period arrives only the next day after having unsafe sex. You need to see a doctor immediately to find out for sure. If you don't want anyone to know that you've been to a doctor, there are free clinics and planned parenthood clinics that you can go to. Please look in your phonebook.
Too much or unsafe speed.