15 week old sleep changes???

My baby girl is 15 weeks today. For the past two nights she's been crying about an hour after she falls asleep at night and then again 30 minutes later and this goes on until about midnight. She doesn't fully wake up so I just put the paci in her mouth. Also she's been having a hard time falling asleep after I feed her about 630 am. What could be going on?? I have gotten so used to her going down at 8 pm and feeding her between 530-630 am then she sleeps again until about 830 am with no problem!!!