Could it be possible that I am pregnant?

My periods are always completely regular, aprox every 33days. I had my period May 15th. I had unprotected sex on May 27th and also again on June 4th. I am not trying to get pregnant, but it wouldn't be the end of the world if we were. I was expecting my period around the 18-19th. No period, took 4 preg since then and all came back negative. On june 22nd I had lower abdominal cramping, not really bad, but since then I've had a clear watery, almost ordorless discharge. I thought it was my period coming late, but alas, no bleeding, just clear watery stuff. My boobs aren't sore, but nipples are really sensitive. Also for a couple days now, i have had heartburn which I've never had a preoblem with. On wednesday night I woke up in the middle of the night chocking because of the heartburn. Today again, I have a bloating feeling like when u have to pee really bad. It's in my lower abdomen only. The last test I took was tuesday, it was a first response early detection one. I have no insurance to go to the doctor for a blood test or exam. I don't want to waste my time for them to just tell me the urine test was negative. I just don't know what to think. I feel as though I am pregnant, but how can I be if the tests are negative.