Help my 6 month old wont sleep?

he did sleep through the night from roughly 3 months and he has been ill recently but he is better now, he has been doing this for the past week, we put him to bed at 7pm and we dont hear a peep out of him until we go up and feed him his last bottle at 10pm ish by 12am he is awake, he doesn't cry or want anything usually. He ust shouts and moans really loud, this will go on and off until the morning, the longest time he sleeps for durin all this without waking is like 15 minutes at the most. I also have a 3 and a half year old wh he is waking every night. i dont know what to do and with my partner working its all really on me to sort this out as he ends up sleeping downstairs as he needs to get a good sleep