With all due respect TC- if you only want to play the game for fun and don't want to devote that much time to it- because we all have lives and jobs, I think- then just play on normal and once you beat it with that character, start a new one- and stay on normal. Or, you could actually ignore the 'advice' of some folks (both here and at Gamestop) and actually play the DLC's and side missions when you want and not at the very end of the game. This will make sure that your character and gear aren't underleveled when you get to the end of the game. But as you say, you don't have to do optional missions for optional rewards- just continue to grind in the main story area missions- Southern Shelf, Three Horns Divide/Valley, The Dust, Tundra Express, Thousand Cuts, Eridum Blight, Sawtooth Cauldron, Arid Nexus/Badlands, Hero's Pass. Eventually you'll get enough XP to where you aren't under leveled (not sure about your gear though- but orcz.com has plenty of shift codes for Gold Keys...).
With all due respect TC- if you only want to play the game for fun and don't want to devote that much time to it- because we all have lives and jobs, I think- then just play on normal and once you beat it with that character, start a new one- and stay on normal.
This is the best answer. This is no need to continue on if you aren't having fun. Everything is optional. Most people playing (this game and others) do just that, and there is no "shame" in it. 99.9% of the people in the world have lives that can't be put on hold for it, and saying you have a life just draws comments from the below types of people so there is no point in stating the obvious. The other .1% (or about 75% of those posting on message boards) have no life outside their particular game, and they let the world know it at every opportunity.
There are lots of sidequests that just give green gear and you don't need to save them for level 50. You can see what rarity item each quest rewards you with by checking(but not accepting) the quest or looking online.
Bottom line- you went in underlevelled and under geared.