If you have 3 subscribers, what did you make? $15. That's not money. And if you make less than that in 3 months on Medium, then those 1.1K aren't readers. Did you do a follow for follow in order to get them? That would explain your low readership.

I wrote an article on why Substack is a very bad idea, particularly for people who aren't professional writers with a strong folflowing.