4 month sleep regression?

Anyone else's LO going through sleep regression?  Does your baby have problems falling asleep all of the sudden like mine?  She will be 4 months next week.    Usually I can put her down awake at night and she will put herself to sleep but for the past few nights she will cry and cry until I pick her up.  Then she'll stop crying, be totally fine and start babbling and blowing bubbles like it's play time in the middle of the day!  It's almost like she doesn't want to go to bed yet!?  I thought maybe she wasn't getting enough milk since my supply is trying to come back after my period caused it to dip, so I gave her some in a bottle and she spit it up like I filled her to the brim!  I got her to sleep by rocking her, which I haven't had to do since she was 1.5-2 months old.  If she was still hungry, she wouldn't fall asleep so easily would she?  Sorry for the rambling!!!  I'm just not sure what's going on or what could be wrong!?  Sleep regression, growth spurt, or something else!?