I'm an average game player and have been able to solo BL2, pre-sequel and BL1....wth are you doing wrong?? Maybe you are over leveled, but what about your gear? If your gear is underleveled, that could be the problem. Edit: didn't see your update until after I wrote this, hope its getting better for ya. You only get stronger as you level, so keep it up.

UVMH can be hard without legendary purple or rainbow items, I've heard

Git gud. Also, Maya for life.

Okay, I’m gonna tell you to get the Bee shield, the most broken shield in the whole game. Good news, if you’re up to farm, it’s easy to get. Bad news, you’re gonna have to touch the Tiny Tina dlc, which has major spoilers. What you do is go through the campaign until you get to the forest, and farm the treants. Eventually you’ll get a shield that adds a flat out damage bonus to each projectile fired by your guns, it’s amazing but broken as hell. It’s the only way I could complete UVHM.

If you have solid guns and use the right elements, you should be able to tear through things, especially in normal mode. Since you're playing Zer0, you might want to change your playstyle up a bit, given his fairly niche skill trees. If you can push through all the way to Many Must Fall, you'll be golden. If you're having trouble with constructors, you might want to spec into b0re, and practice hitting their weak spot with it. Also, a note, since you mentioned getting instantly killed. You can't get instakilled in this game. It's literally impossible so long as your health is above 50%. If you have access to a Moxxi weapon, any healing skills, or transfusion grenades, use them to make sure your health stays above 50%. Also, if Zer0 [i]really[/i] isn't working for you, you could always just start over and try a different character. Salvador is easy-mode, and Maya has great mobbing skills from the get go.

Honestly, it sounds like you're playing it wrong. No seriously. Enemies scale to you, unless it's something like Terrormorphous or something like that. What level are you? What character? What perks are you running on your 'super'? (sorry, don't know what else to call it) Are you leveling up your perks on your baddass points? Are you using guns, shields, grenades, mods, that are up to your level? Are you upgrading you backpack size, number of guns you can run, ammo and grenades you can carry? Do you know how to do this? Are you using the elemental guns and grenades to their strengths on enemies weak to them? Are you alternating slag to the element that hurts that enemy? Do you have a high powered sniper rifle? (does not mean elemental, just high alpha) Or are you just trying to Rambo your way through the game and not playing conservatively when it is necessary? It really isn't a difficult game, unless you're impatient or you are trying to over use things that you should have either put in your vault or dropped. Also, I saw posts about Gold Keys. If you have a facebook or twtiier account, they give out Gold Key codes on there weekly. Sign up, collect the keys, but USE THEM SPARINGLY if you are low level. The Gold Chests give out great gear, but it is at the level you are at. Once you level past it, they're worthless. Save the keys for when you are nearly maxed out. I had like 78 or something when I came back to the DLC. Since beating it, I opened the chest about 45 times and got some really awesome things, and gave many to my son because I didn't or couldn't keep or use them all. The ones neither wanted, we sold to the vending machines for more money.

Are you using elements properly? Corrosive on yellow health, electric on shields and fire on flesh?

What? That never happened to me, and I never play co-op.

If you get the right loadouts, you should be able to solo all the way through UVHM.

Upgrade you bad ass rank or get golden keys sp you can get purple gear