sleep for 14 month old

DS has always been a pretty good sleeper. Have tried everything to make him sleep longer than 5am but he still rises at that time or just before. He is ready for a nap at 8am and will sleep for about 1.5hours and then go back down again around lunch time for an hour or so. By 6.30pm, he's very tired and both kids go to bed then. But lately, DS is waking up through the night? He's not cold, in fact, it is lovely and warm in his room and he's in his grobag and snuggly pj's. He'll wake around 1am or sometimes 3am and scream. I'll go in and lie him down in his cot again and he'll normally go off to sleep. He's 14 months old, for the life of me I can't remember what DD did as she is now 3.5 years but is there anything I should be aware of at the 14 month stage? Maybe he's ready for a toddler bed? Doesn't like a grobag? I'm just so confused and sick of being tired! Thanks for listening and would appreciate some help :o

P.S. he doesn't eat solids really, just throws them on the floor when I offer them to him, tried everything, however, he still loves his toddler formula, have even tried cutting it right down and he still doesn't eat many solids and gets very hungry for milk, thanks!