I'm Worried About What My Body Is Up To! I've

I'm worried about what my body is up to! I've been sick on Sunday night, had on off headache for a week, I'm spotting and having small clots of blood, and have some pain/pressure when I press my lower stomach. I'm on a contraceptive pill but over the last 3 weeks have had my withdrawal bleed and started my next lot of pills possibly missing 1/2 I am seriously concerned I may be pregnant, I have taken 2 tests which have come back negative...