Thanks a lot ! Spanish is so silly with those masculine words that should usually be feminine
Adjective placement in Spanish is not strictly after the noun. There are categories of adjectives that are placed before (such as determiners, numbers, and possessives), and some adjectives mean something different depending on whether you put them before or after. For example, "un hombre grande" is "a big man" [physically] while "un gran hombre" is "a great man" [personally]. "Los mismos problemas" is "the same problems", whereas "los problemas mismos" is "the problems themselves".
It's good to learn that problema is masculine and to make an extra effort to get it correct, because in the U.S. you hear in popular culture (such as films Spanglish, but also on the street) "no problemo." It's "Ningun problema" because problema is masculine. See the comment above about Greek words in Spanish tend to be masculine. El clima, el mapa, etc.
Yeah, that's how I felt when I first started here, after struggling with the same inexplicable gender associations when they tried to teach me French in school.
However, after a year at this app, I'm finding it isn't as hard as I thought it would be, and is really not much different from all the weird special cases we just take for granted in English, but which are probably just as baffling for ESL folks (English as a Second Language).
Keep at it, and it will just become something you don't have to think about consciously anymore.