Breast pain?

So since yesterday, my left breast has been very painful. It also looks bigger and feels heavier/harder. The other one has experienced these symptoms more mildly. I don't feel a lump anywhere either. Anyone got any ideas what it could be? Is it that I started the pill two months ago? Or that I could be pregnant? Or a cyst? Or worse? Unfortunately I'm too busy to go to the doctor right now. Or should I make time to go sooner rather than later?