Two Months Off Three

My son Ollie will be three in April and recently he seems to overreact to everything by screaming, crying and just going mental. I don't understand it is it a phase they all go through?

If things aren't exactly how he wants them to be he goes crazy like earlier his road map was slightly crinkled so he had a meltdown other times if his younger brother touches his toys or even looks at him he starts shouting and crying. He also got in such a state because he didn't want to go to the toilet in his potty beacuse he wanted to do it in a dirty nappy. 
I'm starting to find it extremely hard to cope with now. I've tried talking to him and explaining but it carries on especially when its consistent throughout the day. 

Any advice would be most appreciated.