Struggling

My son is 5 (turned 5 end of August). Since he turned 4 so a little over a year now his emotional regulation is non existent. He gets upset about the smallest things and will cry, scream and yell like he’s a baby. I thought it was just a phase when he turned 4 bc he didn’t do that even when he was 2 and 3 but here we are a year later and it’s the same. And now I feel like my almost 3 year old is copying him and starting to act like him. The littlest things set him off. He gets punished so it’s not like we just let him do whatever he wants. He also talks back now and says disrespectful things. I don’t know what to do feel like I’m failing as a parent. He is already in occupational Thearpy. His teachers are school say he does not act like that at school ( he’s gone to the same school for 2 years). So I know he obviously is able to control it bc he does so at school.