Help! My angel, almost 8 month old turned into a little devil

My son was almost an amazing sleeper. He slept through the night starting 7 weeks old. But for the past two weeks he keeps waking up at night crying. I have to rock him to put him to sleep. Sometimes he will be screaming like someone is ripping his skin off ( not hungry, diaper changed etc) and it takes me 2 hours to put him down to sleep. He has his two bottom teeth already but I think his upper ones are coming out too. But gosh I'm exhausted. Working full time and doing my phd is not helping. Anyone else is going through this ?