i might be pregnant…. im not sure

ive just turned 18 and i had unprotected sex a few months ago- it was with an ex boyfriend. he said he didnt come inside me but since then i havent been having my usual periods. normally i would come on a week after the date i finished the previous month. wierd i know but somehow its the same every time! but for the last two periods since i had unprotected sex i hav only had a light flow only last a day. ive been having some of the symptoms that are on here- ive been feeling light headed with unusual cramps in my stomach. ive been feeling exhausted lately and have been frquently urinateing. i dont kno what to do.