Help with bedtime

So I’m trying to determine if baby is undertired or overtired .. or maybe it’s something else . But bedtime is often a big struggle . I do 2 hour awake windows and LO is 5.5 months . Often the crying and whining starts before the 2 hour is up , so I’m thinking ok time for bed .. I try to keep going to 2 hours but cartoons aren’t helping , we go read a book , still whining . So I think ok it must be time ? Put her down to bed and she’s tossing around , crying , needs some rocking , takes quite some time to get her to fall asleep . Sometimes it’s really bad I have to pick her up (rare) but it’s the only way . I’ve even tried 2h15 before bed, didn’t seem to help. She gets 3 naps a day (3.5 h ) .. so I’m wondering if anyone could help figure out what’s going on at bedtime ?!? Any tips highly appreciated !!