could i be pregnant

OK so i had sex on the 8th & 9th (i ended my period on the 7th). we didn't use protection both times. i've been having stomach cramps, and my pee has been stinging (kinda) just overall a very weird off balance feeling. its now the 20th and it started, i want to say the 15th or 16th maybe. should i just go buy a pregnancy test?