What's going on with my 3 1/2 month old?

My 3 1/2 month old has had a really strange couple of days. She is normally a VERY happy baby and only cries if she is hungry, has a poopy diaper, or is over tired. For the past couple of days she has been very fussy. She even suddenly screamed and started crying a couple of times which scared me. She normally goes... show more My 3 1/2 month old has had a really strange couple of days. She is normally a VERY happy baby and only cries if she is hungry, has a poopy diaper, or is over tired. For the past couple of days she has been very fussy. She even suddenly screamed and started crying a couple of times which scared me. She normally goes down for the night some time between 7:30 and 8:30. She wakes a few times in the night and then wakes up for good at 6am. However, for the past 3 nights she has fallen asleep much earlier (from 5:30 to 6:30) and wakes earlier and more often. She seems to be restless all night as well.

I work at a school and had the nurse check her ears (they are fine). She has just started spitting up often which she never did before and she has been drooling and biting a lot. It seems a bit early for teething and I don't feel any teeth. What could be going on? Any ideas? This is my first baby so I don't really know what to expect and when.
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