Feedback on first PoE character

Hi all,

I am new to Path of Exile and I've gotten to level 57 so far with little trouble. I am currently in act 6, but I am noticing it's getting harder. I think the main reason is my lack of resistances, but I also thought the Witch would be a bit of a glass cannon.

I clear mobs incredibly fast with ice nova, bosses take a tad bit longer, but not super long. Act bosses seem to be a bit harder and the end of act 5 wasn't easy at all and I died multiple times, but I suppose it wasn't supposed to be easy.

I am just curious to see if you guys have any feedback for me that could help me progress further and maybe I'm missing something totally obvious! I've been a long-time Diablo player (1 through 4), didn't like 4 and found out about PoE, which is amazing so far. I don't like to follow build guides and prefer to discover things myself. This is how I ended up with the build I am using now.

I look forward to hearing your thoughts about my character (I only have 1).

Thanks in advance!

Completely normal for your first character. Priority over anything, fix your resistances, damage doesnt matter, if you are alive you will kill it.

Pretty normal.
The game doesn't do a great job of teaching you defenses, so this is quite normal. In Softcore, it doesn't really matter if you die occasionally, but dying repeatedly to overcome something is usually a sign you need to think about defenses, and once you're past the campaign and into maps, you will usually want to make sure you don't die too often - you need a REALLY big cannon to be able to be a glass cannon.
Generally, you want to layer "defenses" a bit. Without a complicated gimmick build, you need Resists and one of Life or Energy Shield, plus a few from the longer list of secondary defenses - Block, Spell Suppression, Regen, Leech, Ward, Evasion, Armor, Endurance Charges, and some Skills. Golems can help a lot - Stone gives a bunch of Health Regen and distracts some enemies, Chaos Golem gives Physical DR. You don't have to go TOO into a secondary defenses, but having them is a great benefit.
I hope that's helpful for planning!