What to do if I have found a lump in my breast and it has been there for 2 or 3 months now. What are the chances its cancer?

See your doctor! It's impossible to quote you a statistical probability other than saying that it could be cancer. Every new breast lump should be evaluated by a physician. Please see your doctor asap.
See Your Doctor. You cannot tell if a lump is cancer. You must see your doctor asap.!
Low but real. The vast majority of breast lumps are not cancer! that should reassure you enough that you will go to a doctor for evaluation! you may just need an ultrasound test, which is painless. In the worst case scenario, if it is breast cancer, the earlier you find it the easier it is to treat and cure...So please make an appointment. Then you can stop worrying!