hi. i think your right to think his tummy is not ready for solids. it seems to be upsetting him. i weaned my first at 4 + 1/2mths using baby rice with breast milk as she was feeding on me every half hour and it was getting a bit ridiculous!!. she started with only a spoon at lunch. my 2nd i didn't give solids untill she was 6 + 1/2mths so each one is different. my eldest is now 6yrs and even back then the recommended age for weaning was 6mths. one of the things they have found is what you have said, that there small tummys/guts are not quite developed enough, maybe some are as they grow at different stages but your having problems so i'd wait as long as i could. another reason hv recommend later is due to all the diets we now have found people to be suffering from, gluten and such, same as everything some will grow up needing special diets others wont but they think it's all about what they eat while weaning and how early they start that effects them.
if you find in a few weeks he's still not satisfied from milk alone and you give it another go you could try just at lunch so he's more active and has time to work it off his tum, maybe avoiding tummy ache so he's not sleeping on it. but it could also be the rice and not solids that's upsetting him, if you get what i mean! my 2nd didn't take to rice, just a thought. you could try the baby cereal.
