My 5 month old doesn't know how to sleep 😔

We got through a week of the dreaded 4 month sleep regression. He was back to sleeping for about 4-5 hours then waking twice but nursing and going right back to sleep. This past week he turned 5 m ok months old and has slept like garbage. I am EXHAUSTED!! He goes down and will only sleep for maximum of 2 hours before hes awake again. I nurse him, rock him, walk with him or whatever it takes to put him back down. Hell fall asleep then I set him in his bassinet and BAM hes right back awake and crying. We repeat the cycle, excluding nursing and hell fall asleep. He will sleep anywhere between 10-45 minutes before he's up again. This continues until 6-7ish in the morning. Last night he went down around 9:30 and was up NO LIE, at least 8 times before 2:30. I need help!!!!!!!! I've started letting him try to soothe himself back to sleep but it is hit or miss. Sometimes he does, mostly doesn't. I dont want to do the cry it out method because we live in an apartment and I dont want to be known as the lady with the crying baby in the middle of the night. Today was the first day i started him on oatmeal. Any thoughts? How do I teach him how to sleep so we both can sleep????