no advice here, but my ds1 is a pita too.... he is 3.5, he has always been like that but we have reached new height recently...
sorry, im not helpful, just wanted to say you are not alone!!
i try to explain him that if he wants something he has to speak with his "man voice" (like daddy, his hero) not with his "baby voice" (which is not baby voice at all more like a very irritating whinging cow's noise... mmmwwwaaaahhhhh!!!!!! mumble mumble mumble mmmwwwahhh, throw himself on the floor, mmmwwwaaaahhh again...)
it is somewhat working, he will now speak a little bit louder instead of mumbling what he wants/needs. at nursery they say "use your words" and i do ask him too.
as soon as he starts whinging, we try (when we have time and the other two DCs are ok) to replay the situation with him expressing himself with his man voice (i do it first, then he has to do it too, properly, looking into my eyes).
it is hard, it really pushes me to the limit of sanity. just now, after two awful days, im tryng to relax and resource myself to be able to cope with tonight. chocolate and coffee are not enough to help me cope.... if you have any tips, im a taker