Lisa, since you've pretty much ruled out other causes, could you perhaps be pregnant? Since you're feeling this on both sides, it would be highly unlikely it's a breast cancer symptom; it's most likely hormonal, from what you describe, and pregnancy is one of the causes of hormonal imbalances. You might also simply be experiencing some "getting back to normal" hormone spikes from childbirth, since your baby is still so young.

At any rate, if this continues to bother you, best to see a doctor, OK? S/he should be able to help you figure out what's causing this, and then prescribe treatment, if necessary. Good luck, and I hope you feel better soon - PJH