Can Drugs Throw Off My Preg Test???help Plzzz!!

Im 17 and im not sure if im pregnant!!! Heres the story......I have been having my period evey 2 weeks for the past several months.Lately ive written down my period days(when it starts/ends).Im not sure when me and my boyfriend last had sex.The last time I would guess is in aug. Sometime between the 20th through 25.I know I wasnt with him on the 26 or 27.(cuz my bf was arrested and now in jail).The last period I had ended on the 17th.On the 29th I would guess I spotted and stopped on the 31st.My period has not come since.Today its exactly 2weeks(1 month if the spotting doesnt count)the spotting was super light.(it wasnt really blood red more like pink)..Ive been really depressed that my boyfriend is in jail so I did tweek and nos.Early in the day.Around 11pm that night I went to the hospital and took a pregnancy blood test. It came out negative.Did/can the drugs throw my pregnancy test off track.These drugs were pretty hard core so did they mess up my test. I really feel that im pregnant.Im really sleepy all the time.It hurts to sleep on my stomach.I either get cramps when I do or get short of breath.I also have to pee frequently and im always thirsty...Could I still be pregnant!!!