Period is late!! Help!!

Hey guys! I'm 18, and married. Me and my husband have been trying, and I have missed two periods. After missing my first period I took a pregnancy test and it said I wasn't pregnant. A week later I took a clear blue test to try to get more accurate, still said negative. Now this is my second period to miss.. I don't wanna keep wasting money on pregnancy tests. Please help. Getting another clear blue today and if it says negative we r going to the doctor. Your thoughts of why? Please and thanks. Have a blessed day. ?