sleeping

My baby is just under 9 months old and his sleeping has not been too good lately. I started back at work 2 weeks ago and it's ever since then really. He started waking up 2/3 hours earlier on a morning but then eventually got back into his routine. But then recently he will only nap for 30mins at a time and we struggle to get him to sleep on a night. Before this he was very good at sleeping. It takes us around an hour to get him to sleep on a night. We give him a feed, rock him a little and then place him in his cot and as soon as I leave the room he cries his heart out!! He has never done this before. I leave him to cry a little before I go in and soothe him and I just keep on repeating this until he falls asleep. He has also started crying in his sleep. Sometime he will wake up from it but sometimes he just cries for a few seconds and then falls back to sleep. He also wakes up a lot through the night crying for his dummy and it is just so exhausting. Any advice?