No period in 6 months, suddenly in pain

I haven't had a period since April of this year. In April however I had two periods, one at the beginning of the month and one at the end. I haven't really thought too much of it because I knew I couldn't be pregnant and my period is usually pretty irregular. I figured it was just stress causing me to miss it. Last night though, like 30 minutes after my boyfriend and I finished having sex I went to the kitchen and get these sharp stabbing pains in my stomach. It got so bad to the point that I threw up this morning from the pain. Since then it hasn't been too awful but there is just a lot of pressure and discomfort in my back that wraps around the front. I know I should probably see a doctor but I can't afford to. Any thoughts?