Could i be Pregnant.?

Hello last Noverber i went on the injection it was my first time on it and i was ment to go and get it again on 30th of January i went a week later and the doctor put me on the pill i took the pill for two days then stoped. Me and my boyfriend have been having unprotected since then and he has came inside me most of the time. I have irregular periods so i thought i probley would not be pregnant. I have started to get really tender and felling tired alot and getting sore heads last week i was getting these really bad cramps that ive never felt before and then yesterday i started bleeding but it was light and did not look like a period the bleeding stated a kind of pinkish/red colour then today its started to go pinkish/brown. But the bleeding comes and go and has only stated two days ago. I was wondering when i should take a pregnancy test as it has been 3 weeks on sunday since i first started having unprotected but i dont now if this is to do iwith the pill or if i could be pregnant am really comfused. And when should i take the test as i have irregular periods. Would be greatful for advice thanks Nicola Xxx