I try to play the game on Legendary as much as I can but if it gets to hard I change the difficulty to Master so it is easer. I am Level 43 right now and I finished all the Companions quests, not much of the main quest line and most of the Mage College quests, right now Im doing the Thieves guild quests and I am Level 43. My Heavy Armor and Blocking skills are 100, should I make them Legendary? If I do doesn't that make me weaker? It resets it back to 15 then I re-distribute the perks, but I won't be as strong right? Since my skill would be back at 15, so you level up your skills again and it goes past 100?

The point of legendary skills is to level up without resorting to skills you otherwise never use.

Your Heavy Armor and Block will get weaker, yes. You'll have to build them back up and re-perk them. They'll stop at 100 again, and AFAIK, you can reset them again if you like (I might be wrong on this detail).

If you can enchant, Fortify Heavy Armor/Fortify Block can ease some of the pain, along with good Smithing skill to make sure your armor is tempered as well as possible.