Hi I am new to this so here goes.

so I have irregular periods so never know when I'm due to get them...me and my bf had sex last Sunday morning and monday morning I noticed that I had a bit of brown discharge...this continued for the next 2 days but not a lot at all..i usually have a heavier period and it normally lasts around 5days and is normally red not brown....I have been having headaches for the last couple of days and feeling a little sick I was just wondering if there was any chance of me being pregnant or not....I already have a 16month old boy and would like to give him a brother or sister....please help!!!!