Baby waking up at 5am and hard to fall back to sleep

The last 4 days my baby girl has been waking up at 4 or 5am not crying at first but 15 mins later after playing in the crib she starts crying. (I observe her playing though the baby monitor to see if she will put herself to sleep again). She's letting out some huge yawns so I know she's still tired. She's also only been sleeping for 7 hours. She usually sleeps for 9-10 hours at night (broken sleep, not straight through). It's hard to put her to sleep around this time even though she's still tired. Once we manage to put her back to sleep she only sleeps for an hour or so. Sometimes it takes an hour to get her back to sleep. Any ideas on why she's suddenly having such a hard time falling back to sleep? She's 4 months and a few weeks now. We have black out curtains and use Merlin magic suit and noise machine.