I am on chapter 12 of Bayonetta and find myself loving it except for one thing. I feel like I can use the same like 3 or 4 combos to kill everything, and I'm not really learning the combo system as well as I should be. I never played any of the DMC games so I'm not sure if I'm missing something. I know playing on a higher difficulty would make me have to string more stuff together, but I feel like that would just make it more frustrating, not in any way better. 
 
So I was basically just wanting some advice on what I should do to try and get better at this style of game. Like should I try and memorize every single combo and what it does so I can better string them together? Because that seems extremely annoying.

The beauty of the DMC games is that you can use your creativity to play the combat system as you like it.. 
 
if the same 3 combos are still working and you're beating everything with ease, then you might want to adjust the difficulty

If you haven't already, use dodge offset, it allows you to hold a combo string while you dodge (you just hold the button of the combo you're on really) and continues your string so you could try new combos and stringing them together, you don't really have to force yourself to memorize them all. As you continue, you'll notice there aren't really that many combos to memorize, because all of the weapons have similar combo strings, but different timing, other than the katana and whip.

Some combos have a few different properties, like PPPKK will sweep the enemies, PPKP will launch the enemy at the end, which both leads to more combo potentials. (sorry if those are wrong, I haven't played it for a while, but you get the idea). The idea is to keep your combo going without having to reboot the string, so you continue to have a good flow with the combat, while staying alert of sound and visual cues for dodging. 

Yea you could literally beat the game with 1 combo if you'd like, that's how the game was designed, the freedom to have as much/less variety as you want.