4 month baby spitting up milk. Four soil diaper in 6 hours. Cranky. No fever. Chewing on everything. Is it teething? Upset stomach? . Should I be worry

Cranky. Your child could be teething but is a little young yet.. He may be in pain as a result of gas being produced by your baby's loose stools.
Teething/reflux. Gagging on saliva and perhaps a bit of reflux with teething may be contributing to your events. I would approach this with smaller feeds that do not overfill your baby's tummy. Rub the gums and maintain upright postioning after feeds. I would not use medication at this time since this might make the lining of the stomach irritated.