So I had sex with my boyfriend after my period ended. Now a week later I'm having brown discharge and my lower abdomen is having cramps
I have a headache
I have back ache
I never throw brown discharge before so I know that's not a normal thing for my body

So your period ended a little over a week ago? It would be too soon for any symptoms of pregnancy to manifest themselves. Are you pregnant? No way to tell at this time, its too early. You need to wait until your next period id due and see if it comes. If it is lae for more than week then you can take a test.

If the symptoms you are experiencing persist, see your physician.

Unprotected sex? Trying to get pregnant?

How long after your period did you have sex? When is your next period due? It's possible that it is due to pregnancy, but you'll need to wait and see what happens when you would expect the next period.