Sorry to hear you aren't getting much sleep. Neither am I and my little girl is 10mths.... she started going 'off' her sleep around the same age as your DS! She used to sleep really well at one stage like 7 to 7 only waking once or twice and now she is only sleeping 2-3 hr blocks at a time.... feeding alot too in the night (she's BF).
Teething has something to do with it I know that, well in our DD's case.... but yeah her sleep went funny around 7mths and has been even til now.... I'm STILL waiting for her to settle down again into some sort of routine!
Sorry not much help.... just go with it as best you can..... we've started co-sleeping just so we can all get more sleep.
These babies like to surprise us don't they?! Just when we think they are getting predictable, they change on us!