Sounds like teething to me. But do consult with your doctor or check out this guide: https://sg.theasianparent.com/the-go-to-guide-for-your-babys-teething/?utm_source=search&utm_medium=app
My baby is 2mo plus almost 3mos. She is also not drinking enough milk. I prepare 90ml for her but she only finishes 60ml every 3-4hrs. Sometimes she prefer to sleep.