A few thoughts:
Yep, kids are born with a variety of personality traits. Sometimes these traits become more pronounced as the personality matures.
Sometimes when personality becomes "more" or "less" of some characteristic over a fairly short time, or when the personality appears to change in some significant way, there is a physical cause. Ear or tummy issue?
Another problem that's becoming alarmingly common is toxic exposures to the myriad chemicals we live with today. Many household cleansers, laundry products, air fresheners, etc., are loaded with toxic ingredients which can cause physical symptoms, mood changes, or both. Some figures suggest that more than 1 child in 5 is now affected negatively by chemical exposures.
Your son will almost certainly scream less when he's able to communicate more. It's incredibly frustrating to want something that you can't manage yet, and not be able to even express your misery with words. The MOST wonderful and helpful book on the subject is How to Talk So Kids Will Listen, and Listen So Kids Will Talk, by Faber and Mazlish. It won't conflict with anything the parents do, and the wisdom in this book will make it a resource you reach for again and again. We've use these techniques with my 6yo grandson for the last four years, because they work brilliantly.
Just one example: Punishment for unacceptable behavior, or physical rewards and charts for good behavior are not as effective as when adults remark with calm admiration when they see the child do something positive. Examples are, "I noticed how carefully you put that together." or, "That was hard to do, but you kept trying until you did it!" or, "It felt so good when you told me thank you." or, "Hmm, how did you figure that out?" or, "I see a boy who picked up his game without being asked." or, "You chose your outfit today? I like those colors together." or, "I'll bet you can figure out a good way to do this – will you please help me?" This book will coach you on ways to deal with YOUR particular child's needs. Try it – I can promise you'll like it!
This is only one of numerous tips and techniques – there are ways to get the child involved in solving his own problems, ways to present your needs to him so that he can recognize and respond positively, ways to find "natural" consequences for mistakes, and more.
Using this book has eliminated the need for virtually all punishment from my grandson's life. He'll occasionally take himself into a sort of time out when he needs to get his emotions under control, but that is his choice. He's polite and cheerful, and super-motivated to be part of a family team, because he understands the family is on his side. I think you'll agree that How To Talk/Listen could be the best investment you've ever made when it comes to working with kids.
Wishing you well!