Possibly pregnant???

I've had a super light (the total amount wouldn't fill a single tampon and it only lasted two days, if that) very dark, almost brown period for two months in a row. My lower back is killing me and I've been nauseous every day. My boobs aren't particularly tender but they seem a little bit bigger than before. I don't know if I'm just panicking. I've been on the pill for almost a year but I have had sex without a condom multiple times. Should I take a test or am I being paranoid?? Has anyone had a similar experience??