Pregnant ?

I'm on the pill, so my period always comes on time . I missed one pill last month. Af never came . It's been two weeks . I took on hpt and got a negative ?  I've had symptoms, enough that the people I'm around often wanted me to test again. I'm also underweight, not a lot . ( no I don't have an eating disorder , no I'm not sick . I'm just thin . Always have been .)   What do I do ?