Hi, my little boy has gone from sleeping eight to nine hours with one night feed to waking up two hours after going to bed and then four to five later. The first wakeup seems to be the most restless and the hardest one to get him back asleep. He's 10 months old.
There's a big developmental leap at 10 months and this often coincides with resistance to sleep as well as an increase in night wakings, many of which are very intense. During these leaps babies will have an increase in developmental frustrations, which they often release at night in big overwhelm cries. Not fun for anyone!
I suggest you think about how you're responding to his cries during the day. Do you pick him up, rock him or try to distract him? If so, try getting down to his level, looking him in the eyes and supporting and validating his feelings.
In terms of his daily routine, now that his body clock is established you might find it easier to stablise his naps and bedtime by the clock as opposed to relying on his sleep cues. Of course each baby is unique and has their own individual sleep needs, but an average 10 month old will typically nap twice a day. They might follow something like the below:
9.30-11.00am nap 1
2.30-4.00pm nap 2
8.00pm in bed asleep
I know this is only scratching the surface but I hope it gives you something to start with. Please remember you are doing an amazing job and have not caused him to start waking up!