M.L.
HI. My son is 6 months old and I am breastfeeding too. What I have found is that if I wear a REALLY supportive sports bra (or two at once)- I can work out. I use the Frog Bra from Title Nine (online company or in Oakland). It isn't a nursing bra, but I just change when I get home. Granted, I am a 34 but I am an E and I can even run with this Frog Bra on.
Hope this helps!
M. Land