Sleep regression?

My daughter is 5 months and was a great sleeper from the start. She would sleep through the night and only wake up once to eat then go right back to sleep no problem. All of the sudden I can NOT get her to sleep more than 2-3 hours at a time. She keeps randomly waking up, sometimes nursing helps, sometimes not. She goes back to sleep, so it's not like she just a wants to be awake.  I feel like we're back tracking and I don't know how to fix it. Any ideas? 
PS- when we put her down at night, she puts herself to sleep. Same with naps during the day. We rarely rock her to sleep anymore.