Introducing solids--advice please!

So my LO is 5 months and I gave him less than 1/4 teaspoon of pureed veggies the day before yesterday and yesterday I put 1 teaspoon of oatmeal cereal in 0.5 ounce of breastmilk and he really did not eat the whole thing. On both days he was straining himself, grunting, and kicking his legs up and down. It also kept him awake at night which was hell for me since I have work. He had a bowel movement twice each day and really he had so little of the solids and oatmeal cereal that I didnt think it would affect him this much. I do feel like he's sensitive because he did this often even in breastmilk. Is anyone else experiencing this or have any background on this? Gas drops were not effective by the way. I'm reluctant to even continue giving him anything besides breastmilk. Advice please