This happened to us at around 3.5months. Can't offer any advice because it is still happening. I haven't slept longer than two hours straight for 3.5months. The only way I can survive is to have him in bed with me so I don't need to get up to him, can just feed him back to sleep. I have tried patting etc but he just gets louder until he gets fed.

During the day I have to feed him to sleep and he will wake after 1-2 sleep cycles and I have to feed him again to get him to resettle.

Hope that you find something that works for you.