Oh man, do I know how that feels... and I'm not new to exercise! I think half of the time when I re-start a weight loss plan, I overdo it. And almost every time I try a new exercise!
I've lost count of the number of times I've planned to run a certain distance, with a certain number of walking breaks, and gone wayyy overboard, only to have my shins and feet hurt for weeks. And you should have seen my first spinning class... I was completely DEAD by 20 minutes in (to an hour long class) because I had worked so hard. I could barely walk after my first kickboxing class.. and the only reason my upper body was intact is because I just literally couldn't do half the exercises (push ups on our knuckles on a hard wood floor?? I was ready to tell him where I wanted to put that punching bag!

).
I guess my point is, start slow. And when you branch out into other exercises, start those slow, too. Or if (heaven forbid) you find yourself having to re-start... well... re-start slow.
And a big congrats on the weight loss so far, that's great!