This started happening to my DD when she was 3 months old too...her naps were finally going well, and then she started waking more during the night! What this told me, was that she was ready to be moved to the 3 1/2 hour EASY. Everyday, I would add 5 minutes to her awake time, gradually getting to 1 1/2 hrs awake, 2 hrs sleeping. My little one is now 4 months old and we are working towards a 4 hour easy now. I found that once she was awake a little more during the day, she stopped waking more at night. However, the first little while on the 3 1/2 hour EASY, it was a hard adjustment as she still was sleeping a LOT during the day. However, we started putting her to bed earlier and thus no more evening catnap and that helped too.
Hope this helps.
Lori