I had the same problem with my son about that age. He is going through a growth spurt and needs a little more now than he did before the cereal and sweet potatoes. What we did was increased the amount of formula during the day, fed him his cereal and then his jar of food. Then right before bed, we fed him a bowl of cereal along with his bottle. It really helped. Try increasing the amount of cereal you give him, and I would go to the stage 2 jars of food for dinner only for now and slowly increase it when he starts eating the whole jar in one sitting. I would increase only by one to two ounces at a time, to avoid him not eating all of it. If after a few days he is still hungry all the time, increase it a little more, until he is totally satisfied. Don't worry about him gaining too much weight right now. As my Pediatrition said, "when he starts crawling and walking and then running he will wear off the extra weight and it will all work out as long as he is active (then take him to the park daily and let him run!)". It is very healthy for babies to love new foods!
Just experiment and think that at least he is eating. Good luck!