Dealing with unrealistic expectations is one of the biggest pieces of advice I give to new creators. Look, lots of normal readers won't sub to a brand new webcomic, just because it is a new webcomic - most webcomics die before their tenth update.
It helps a lot to find some comic peers that you can track with. Pick two other comics that started about the same time as you, in the same genre. Ideally you'd get one that's better than you and one that's worse. Compare your stats against THEM, not Litterbox comics, The Little Trashmaid, or Punderworld (or whatever). If they outperform you, then look at what they are doing that you aren't, especially if the one you think is worse than your comic is outperforming you.
In my case, I left both peer comics in the dust long ago. One stopped updating quickly, the other never went anywhere. So then I find some new peers to work against/learn from. It's like running in a big race - don't worry about 1st, just worry about the guy in front of you. And if that short guy with stubby legs is outpacing you, figure out what he's doing and whether you can do it, too.
In the first 3 months, I had 30 subscribers. I didn't use the forums then, and I never did make it into a community feature or anything like that AFAIK. I posted my comics on Reddit and DeviantArt and that was about it for promotion. So compare against that. I was thrilled with 30 - my expectation was 1/wk or 4/month. I had some months close to that for a while! The perseverance for webcomics is hard to learn - it took me over a decade to be disciplined enough to keep a longform webcomic going.
Realistic expectations and peer pace-setting will go a long way to making sure you don't feel disappointed in not getting 10k subscribers on a 4-update comic. That doesn't happen to anybody, at least not to anyone I've ever heard of.
