Diastasis Recti

Hi all, had baby #2 6 months ago and this time around I had a 4 1/2 finger gap postpartum. Yikes! I've been doing DR-friendly an exercises to close it and I'm down to a 1 1\2 finger gap (woohoo!). My question is: I feel like my tummy is still so weak and building lean muscle seems impossible. Normal??? I don't want to re-injure myself and military healthcare won't cover surgery unless it's a serious problem. I just feel like the exercises I'm doing aren't helping tone my midsection sufficiently.