My first son was like that. He would wake up every few hours and scream and scream and scream! I was not able to let him cry it out until he was one and by then it was too late. We tried again and again to let him cry it out and he would cry until he would projectile vomit over the entire room. It was so awful. He has a tenacious personality and would outlast us. In the end he didnt sleep through the night until he was 3 1/2yrs. Looking back, I realize I needed to be stronger and do sleep training much earlier, but I didnt have it in me.
I was much more on the ball with sleep training with my second son and let him cry it out at 5 months (well, I got my husband to do it because I physically cannot hear crying and not respond- I wore ear plugs) It actually worked in 3 days and he is a great sleeper. My husband slept outside his door and would check on him. When baby woke, DH would wait 20 mins to give him a chance to go back to sleep on his own. When baby would cry longer, he would go in, rub his back and tell him gently it was time to sleep and then leave the room right away. (i don't think it would have worked as well if I had done it as DS is also exclusively breastfed and would want to comfort nurse if he way me). Gradually he woke less often and cried less and was able to put him back to sleep. DH kept a log of everything so we could see improvement and to reassure me of the process. I let my husband sleep all day because he was seriously up all night for three nights. I also think it help my second bond with my husband because he got used to being reassured by him and how my husband can put him to bed without me.
My best advice is to get a plan to sleep train and don't stop until he gets it. Be consistent. Don't give in if he cries for just an hour, or two or three. Going in, very briefly in intervals to reassure (NOT PICK UP- just a 5 second back rub and calm whisper-"its time to sleep".)
I wish someone had given me this advice with my first and told me that it was really ok and life will be so much better for the baby and for you. It is such a different and wonderful experience having a baby that can sleep through the night and I feel sad that I didnt have that with my first. I was such a sleep deprived wreck that it impacted my ability to function as a mom and have quality time with my first baby. I look back at his first 2-3 years as a chaotic blur as opposed to baby bliss. Seven months is till young enough for you to avoid my path! (assuming he is healthy and has no feeding issues etc.) Get help if you need to- if you can't do it, get your husband or mom to do it. Best luck!