feeling my heartbeat in my uterus and other symptoms...pregnant?

i've heard this is the blood flow getting stronger preparing for pregnancy...are there any other explanations? also,i've been on yaz for about a year now, and i've never had any problems with it. This month i took my pill late twice, but i did take them the next day. I've taken my pills late before and never had a problem..when i wasn't having sex. My boyfriend and i don't have sex very often, but for the last month or so we've been having more sex than usual and one day out of no where my armpits started getting sore really close to my boobs, and then about a week later i started getting a little queasy.. I never have strong PMS symptoms. I started my period early.. before the yaz placebo pills even started, and it hasn't been extremely heavy but more watery or dischargy and dark brown (sorry kinda gross). and its lasted about five days and my normal periods only last about two. i've also been having heat flashes where i feel like i'm getting a fever...it's just weird. i may just be worrying to much since its almost impossible to get pregnant on birth control, but i want to ask anyway..