As Michael said you really need patience. It’s really a long long game.
The more tunes you know, the easier it gets to learn new ones; so I suggest you try to add a new tune every week, or something like that. At one point things will just click and you’ll suddenly realize you can learn tunes much faster.
Another thing, if you have a chance, join a local session. You don’t need to play at first, just show up and listen to the tunes, that’s the best way to commit them to memory. I’ve been playing the fiddle for years and had no session pals at first, so my repertoire was around 80-100 tunes and it stayed like that for 10 years or more; when I started joining local sessions the number of my tunes tripled in 2 years time, with much less effort. Now, after years of practice, it takes a few minutes to learn the basics of a tune on the fiddle; probably 20-30 minutes on the concertina but I am really a beginner here.
Final advice, play very slow. Everyone says that, and it made little sense at first but now I can tell you it’s the only way to get a good rhythm.
Again, patience, and enjoy the ride.