Could it be that its not picking up on the test or i am just not pregnant?

i have had unprotected sex and have been having alot of pregnancy symptom for months but still get a period like bleeding thats not regular as most times it comes as spots but each time i take a pregnancy test it comes back negative. could it be that its not picking up on the test or i am just not pregnant. also recently i felt a kick to my stomach but was told that its because i was cold why i felt that way. as we speak i have been getting spots like period for one whole week and still counting and also a sense like fatigue where i can hardly sleep. BUT my tummy have not grown an inch...... NB i have been watching on discovery health where persons are pregnant and didn't even know until delivery day and these symptom i am experience is similar to most of them and also their tummy didn't grow either could it be the same thing i am experiencing or its just my imagination. but note well that i started having these symptoms before i became aware of this and my boyfriend was told by a doctor that he cannot get a lady pregnant and so we always have unprotected sex.. i know something is going on in my body if am not pregnant then i must be seriously sick. i am worried and need a response asap