Hi there! I completely understand your problem. When I started my webcomic, Outcasts, I had NO readers for a while until the first few readers got hooked and decided to stick around. I'm not gonna lie, though; during that period of time with little engagement and was lucky to have ANY readers at all, I'd be lying if I told you it was hard to stay motivated and even pick up my drawing stylus.
My suggestion: From what I've experienced and what I've heard from fellow webcomic makers, here's my advice: Make the comic you like and like to create. You like fantasy? Make a fantasy webcomic! You like characters finding themselves? Have your main character go on a self-discovery arc!
The bottom line is this: It's going to take a while for your webcomic to get out there. If you only rely on extrinsic motivation (in this case, reader engagement and people subbing to your webcomic), you're more likely drop the webcomic and its story entirely. Your love and passion for making your webcomic will drive you forward more than anything. Keep going and don't give up! I believe in you!
Keep creating & never give up,
Cookcakez357