Sore breasts...prego?

My husband and I have been trying to get pregnant for about 8 months now. It's was an emotional rollercoaster ride with all the negative tests we were getting. So a couple months ago we decided if it happens, it happens and not to focus so much on it. My breasts have been sore for the past 3 - 3 1/2 weeks. This morning I noticed that my nipples were more sensitive than usual. My right breast's nipple felt like is was burning . Its an off and on burning. I havent had my period, but I had a manditory pregnancy test a week ago and it came back negative. There's a lot of money going toward bills right now and prego tests arent cheap, so I want to make sure there's a good possibiliy before I buy tests. So could I be pregnant??? -Heather