Possibly pregnant?? At first i got negative then a positive then a negative

I had sex in October and took a few pregnancy test a week or two after. At first i got negative then a positive then a negative. My period was over a week late when i had some bleeding. Ive only had two since i had sex i believe. And i do have symptoms. And my stomach is a bit hard. when i lay down or sit still i feel weird movement in my stomach. I get nauseous at the smell or sight of certain foods or the smell of anything really . I took two Walgreens brand tests last week but one didnt work and the other said negative. What should i do????