120kg walking hard to lose weight + not getting tired + having heart skipping ,walking like 2 hours fast with a lot of up hills im i over exercising ?

Over exercising: Hard to say if you're over exercising, but I will definitely say you are doing the best you can physically to lose weight. Be sure you're complimenting your activity level with controlling your oral intake. If you use up calories, but make it up by consuming a lot after a heavy work out, then you're not really helping yourself. Make sure your diet is well balanced. See a nutritionist for advice