The problem you're dealing with is pretty common on the coast - humidity makes any base dissolve. Fit Me is decent but it has a lot of water content, so in humid climates it's basically impossible to make it last. What actually works better for oily skin in those conditions is a base with a drier formula, like ones with silicone or long-wearing ones. Look for something that says "long-wearing" or "oil-control" on the label. Catrice or Essence bases tend to be pretty affordable and hold up really well against heat and humidity, though you'd have to check if they sell them where you are.
What I'd do besides that is change your whole prep routine. Before applying base, use a primer specifically for oily skin (it doesn't need to be expensive, a good gel primer from any brand will help), and please use a setting spray after you're done with makeup, not just powder. Loose powders alone aren't going to hold without something to set them. That's what makes the real difference. And here's the weird part but it works: some makeup artists use setting spray in between layers, not just at the end.
Also think about whether you could maybe use a powder base instead of liquid straight up, or a lighter BB cream with a lot of compact powder on top. In climates like that people often get better results with less product and better setting than trying to use super full-coverage bases that just aren't going to last.