im on the pill but think i might be pregnant will the test be accurate?

I've only been on the pill for nearly 2 months, prior to this i had sex a couple of times, using a condom, but im pretty sure it broke last time or the time before, which were about 2 and 4 weeks before i started taking the pill.

i've been really exhausted for the past few weeks and am going to the toilet alot more frequently (about 8 times a day, compared to a normal 3 or so), i've put on 3 and a bit kg in the past 3 weeks (and as i was only 49kg and have always found it difficult to gain wait, im naturally a bit worried) also my breasts have gotten bigger ( and im only 17 and have always been slow in this area of development, so this also worries me). I my period has come as im up to the 'sugar pils' but for the past 2 timess it only came on the 3rd 'sugar pill'. both these times its been relatively light.

i just got my period today- and i now that would generally mean no pregnancy as well as the fact of being on the pill- but im really concerned, and as im so young pregnancy isn't yet on my 'to do' list in life.... I want to take the test but im very worried that being on the pill will automatically give a negative reading...

Is this what the pill will do to the test? or will it work as if i was not on the pill??