Try to figure out WHY you got subscribers, and roughly when the intake of subscribers stopped. Then you can probably adjust SEO or the content itself to get more subscribers.
This is only a suggestion, so you don't have to take any notice of it.
you are not gonna gain subs everyday, or maybe every week, especially when you are still small your videos aren't seen that often and most likely not being recommended on youtube's home page, just keep making videos and keep advertising