M.D.
I'm glad he slept so well while you were alone for 3 months. At least you have some help now. I would stay away from the rice cereals as they aren't a very healthy food and are constipating and also not more filling than breastmilk or formula. As a previous poster said, you can try to offer more table foods during the day, as well as milk. Then if he is waking because of hunger, you may be able to reduce that.
But, there are many more reasons he could be waking: teething, separation anxiety, working on a developmental milestone, etc. Sleep isn't linear meaning that they may sleep very well for a while and then may wake more often. This is very normal and I would say your baby "isn't" sleeping through the night anymore rather than that he "won't".
Good luck and this too shall pass!