Don't worry. We all go through this. I've been making my comic since 2012, posting it on Tapastic for a year and my following is growing very slowly.
I even feel it's plateauing right now...
When I just had my website, only friends and family would read it. That would be 1 or 2 readers per week max!
Let's face it, humoristic, one page self contained comics works better online. And a lot of artist spent year mastering their craft and building up an audience on other platforms.
But I believe there is a space for long form comics too. Just take more time for readers to get into it.
Two things that helped me grow an audience here:
-Interacting with other creators through their comic, especially the ones with the same or lower popularity. Find that hidden gem you can support. Help others and they will help you.
-Being active in the forums. Since you're here you know. But there are all kinds of events and game going on here. Just participate and don't forget to include your links and images when appropriate.
Hope that will help. Don't loose hope. It's normal to feel down sometimes. Happens to me too and to a lot of others I'm sure.
Draw comics for you first!
And focus on the few readers you have.
The only ones that fail are the ones that give up.
Webcomics is all about consistency and endurance.