as the others have said a bit of "me time" will work wonders. During the day if you can't get a break can you just pop him in the pram and go for a walk, I know if you're tired you may not feel like doing that but it may re-energise you a little and you can always take a picnic blanket, go to a park and just let him crawl around a bit while you sit and chill.

Also letting him play with toys/books on your bed while you lie down and have a bit of a rest, or sometimes I let DD play with the toys in her room and lie down on the floor with my head on one of her big stuffed toys (quite comfy!)

Have you got a teething necklace for him? Don't know if it's something you would be interested in, but I got one for DD, she has been wearing it since Saturday and the last 2 nights she has slept really well and had quite good day sleeps too (in that she has gone to sleep straight away instead of an hour or so trying to get her to go to sleep). I don't know if it's the necklace or if she's just decided it's time to sleep, but I'm thinking it's a fairly big coincidence!

Hope he starts sleeping better soon.