How far along were you? I'm wondering if it might might be something to do with breast milk? If you were quite far along then perhaps your breasts had begun to produce milk and now they're settling down. That's just a guess!

Otherwise, I would say it's probably just an hormonal thing. Sore breasts are a common PMS and pregnancy symptom so it could be that your hormones are all out of whack and just need time to settle.

How many weeks were you when you had your abortion and how long has it been since then?

The simple answer is that it is your hormones. You are not making milk unless it was quite late in the pregnancy 6 months and I doubt you were that far along.