J.G.
One thing that happens when baby starts to eat is the digestive track starts working more and that may cause discomfort, gas, new bowel movements. Its normal & will pass.
Baby is waking up too much & most likely not because they are hungry. Have you tried to coming in and rubbing their back? Pacifier? What happens if you don't go to baby at 8:30? Normally it would pass in 3-5 minutes and they go back to sleep.
I highly recommend Dr. Weissbluth's book as well.
Not a personal fan of cry it out technique but there are ways to cut it out or at least minimize all that waking! We are down to 2x from 4-5x!!
Also teething is probably happening too! This too will pass!
Best, J