What have the Preschool suggested so far @Maybe87? Have they suggested seeing your HV or getting their SENCO to have a look at him?
Is he going to school in September?
I think the first thing to do is to check his speech and language is on track. My DD has issues with SLT that aren't always obvious.
I'd do this progress checker from Speech & Language UK. It will tell you if he needs some support and you may be able to book a free appointment with one of their Speech & Language Therapists.
If it does say he needs support with SLT, I'd ask your HV for a referral for a referral for SLT and a hearing test. The Speech & Language Therapist will want him to have had his hearing checked to rule out Glue Ear.
I'd also tell your HV that he's struggling at Preschool and you'd like to see her as soon as possible.
Fill in the Ages & Stages. You haven't said exactly how old he is so you might need to search for the correct one 
Also fill in the Social & Emotional Ages & Stages and ask your HV to mark both of them together. Doing both will govern her a better idea of what's going on and if your DS does need a referral to a Paediatrician for assessment. Again though this might not necessarily the correct one so you might have to search for the ASQ SE that is for his age.
To help you with his behaviour I'd read the Explosive Child.
I'd also try and get him something like Eggspressions and a book like My Many Coloured Days. Your local library should have a few books on feelings and emotions for this age though.
Don't worry about where he sleeps for now, if he's getting some sleep and so are you that's good. If it does turn out that he does have ASD they may prescribe Melatonin but that might not happen for a while as the wait for assessment can be very long.
You might want to head on over to the SN Section too and ask about ECHPs, what they are, what they can include, how to get an effective one and what you can try and put into place before he starts school. He doesn't need to have a diagnosis of anything to have an ECHP, just a need for support which if he's so distressed at Preschool or sounds as though he has 