Is it because you're promoting what videos you have and not getting anywhere? Cause I mean.. you've got 4 videos, and you're posting around one video a month, for you to have even 120 subs with that kind of lack of content is actually pretty dang good. I started out posting around 2 or 3 videos a week and I think it still took me almost a year to hit my first hundred subs. Things picked up after getting over the 300 sub hump but I'm pretty sure it was a slow slow climb to 300. It's hard to remember I quit making content around 3 years ago.
But yeah I mean, if you want more subs you gotta give em more content! You know I was at around 800 or so subs and was climbing steadily when I started to let nerves put distance between my uploads. I went from a few videos a week to not uploading for a month or so and my views and subs went to a dead stand still immediately. This is just one man's opinion but I feel as if it's like starting a fire in the woods. It takes time and persistence to get the thing started and then once it's going you gotta keep feeding it or the dang thing will go out. Hope that helps