I want to gain weight HELP!!

I’m looking to gain weight, and I live in a small town where there’s one gym, and that gym charges $175 a month (too much for me) I mean I have the finances but that way you to much!!! Anywayssss, I’ve recently started taking a weight gainer (mass gainer) but I feel like it isn’t working. Any tips to help with gaining weight? The biggest I’ve been was 120 when i was pregnant with my third child and even after I was a perfect weight due to birth control.