First and foremost understand that you are not the only one going through this. We all go through it. The scale is different, but this issue will never go away. You will experience times of feast and times of famine when it comes not only to subscribers but views, CPM's, sponsorships, content etc.
The good news? This can be fixed!
You do well to have your subscribe Call to Action towards the beginning of your video... but I don't think you are applying it as well as you could be. Currently you begin your video and almost immediately jump into your CTA. This isn't working; if your audience is accustomed to that being the beginning of every video they are going to get bored and complacent and new viewers are going to hear this and likely shut down almost immediately. Viewers have been sooo inundated with 'Please Subscribe to my Channel' that they don't even pay attention to that any more. Furthermore, you have not given them a reason to subscribe. You simply ask them to subscribe for the sake of subscribing.
I suggest you make two adjustments to your CTA. First, get more creative. Figure out a fun and creative way of requesting the viewers subscription. Laura Kampf, Whang! and Leon Lush are three good case studies for unique CTA's. Second and most important... you need to provide value. You need to give the viewer a reason to subscribe. instead of leading off with that at the beginning of your video you need to start your video with a solid reason why the viewer needs to watch this video, and that they can get more of this if they subscribe. Rest assured; your subscriber count is going to live or die based on the value you provide. Give enough value and you won't even have to ask them to subscribe.
