As a Mum of a 19yr old severely autistic teen with learning disabilities - I'd like to agree most people have covered all your options.
Yes it is very hard work & often heart-breaking, so you need help! Family is great, if they practically support you, real friends to listen (& help in small ways), ask the school about attending an Earlybird course [the basics] & should run a support group & sessions (get to meet others in the same basket) & their support/everyday chat can be very useful & normalising - we were all clueless beginners once.
People keep mentioning social workers etc. but they do have huge case loads; your local Carers Centre have a lot to offer - can support you in giving you local information, writing letters, doing those crappy forms, & being there with you for meetings with professionals - generally having your back.
What has been left out is your local GP (the ones you gel with best) - use them, book regular appointments when you feel down & overwhelmed, they will talk through things with you; & they can put pressure on Social Services/Health & Education. They can also get to know you & your child, take him along with you. You can always ask for a double appointment for you & your child/children!
About the screaming - that's usually down to frustration & not being able to communicate with you. Get back to basics e.g. baby talk i.e. more, drink, food, sleepy time, singing/music is very soothing. PECs worked for my son at school, but I was too undisciplined at home, but he does understand more words than we know - so keep on trying. Mine is now saying 4 word sentences occasionally when it suits him, others start much earlier (yes, it hurts that others are more able - but that's life & life can be tough).
When you guys get those good & funny moments hang on to them. There will be many more with time.
Take care of yourself - we can only do our best under the circumstances & you are a 
. Try not to isolate yourself, go for very short walks with him (or alone when they are in sch) - cos' we all need a bit of fresh air & the odd treat
.

PS. In my loneliest moments over the years, I have called Samaritans many times - who are great at listening, & available in the early hours free of charge.