If you're still playing a Normal mode character at level 35 and have finished the main story line, switch to True Vault Hunter Mode, then start back through the main story. You will find that you gain the next few levels relatively quickly. This is because you're no longer straining to get XP just from killing baddies. You're completing missions, which gains XP much faster.
The Hammerlock's Hunt DLC is particularly difficult at level 35 in Normal mode, even though it's supposed to be scaled to level 30+. I gave up on it until I got my character up to level 41/42 by playing TVHM for a while, then coming back to Hammerlock's in Normal mode. I rarely use launchers in BL2, but for witch doctors, out comes the launcher. Homing area-of-effect grenades are also good, because witch doctors move slowly most of the time. Witch doctors have a fast-move mode, usually some kind of tornado form; when this happens, don't try to hit them, just run away. Use the time to reload and let your shields regenerate. The spheres are also tres difficult.
I just completed Hammerlock's again in TVHM at level 52, and found the going a lot easier.
I found Tiny Tina's DLC a bit easier to handle in the mid-30's. The most memorable difficulties I had were dodging skeleton arrows. Through some miracle, all BL2 baddies using thrown weapons — grenades, arrows, spears… — can not only throw them with uncanny accuracy over great distances, they can even do so when there is an obstacle in the way. This doesn't prevent them from knowing exactly where you are! BL2 baddies also have the wonderful ability to make grenades stick to the ground right where they aimed them. So: learn to dodge and jink!
Once you've gotten a few levels up, you can go back into the DLC on Normal mode. You'll find things a little easier now. There is no penalty for switching modes in Borderlands 2. Your inventory stays the same between the two modes, your XP stays the same, etc. All that changes is the mission progress and the level of the baddies in each mission. If you save a Normal mode character in an area of the map that your TVHM character has also unlocked, you will even start back up in that same area when you change modes.
Finally, when you're running into a difficult patch, switch to another DLC or mission, one with a lower difficulty rating. Killing the baddies in that lower-level mission won't get you a whole lot of XP, but you may find an item that will help you survive better, and the mission completion XP will still be substantial.
Oh, one more thing: consider respec'ing your character. At level 35, you should have most of your points in a single tree, and have that tree almost completed. If you have them spread across all three trees, it means you are missing high-level skills that you need now. It's okay to grab a few of the top-level skills in the other two trees, especially when it helps you make use of a character mod's bonuses. You can start filling out a second tree at level 30-35.