My not-so-little guy is 18ish pounds at just about 5.5 months (not sure how many weeks that is, somewhere around 22?). Anyway, he does wake most nights for a night feed after sleeping through around the 3-4 month mark. He seems to have many growth spurts (many more than "the books" say he should), but he'll go through nights of needing to eat and then I'll have to go buy him bigger clothes (yet again). With the randomness of your night wakings, hunger could definitely be an issue. I find that my ds settles himself is able to settle himself sometimes, but if he cries it's really only feeding that gets him back to sleep.
If he's trying to roll, there's not much you can do, other than give him the opportunity in the daytime to practice. It will all come together eventually!