Worried about breast cancer

For the past couple of months I have been suffering from an intermittent sore area under my right breast. GP suggested new bras and gave me ibuprofen gel. It seemed better but now has returned. It's really strange as some days it isn't there at all and others it is so tender I can think of nothing else. I'm 64 so it can't be hormonal. Anyway today she has referred me to the breast clinic and obviously I am now very anxious as to what it could be although she did say it wouldn't be flagged as an urgent referral as it isn't typically cancer. I have racked my brains as to what else could be causing it but can't think of a thing. Has anyone else out there had a similar experience?