Any tips on road bike will be appreciated. I'd like to know mainly about keeping balance. I have a new bike. I've used it once last week and my body was super tired the next 2 days. (2 miles only). It is way different than a mountain bike. Why?

Road biking is different from Mountain because the bike is lighter and speeds are faster, which makes balance a little different. How often do you ride your mountain bike? More than 2 miles at a time? Not sure why it wore you out so much, are you in good shape? I say keep riding it and you'll keep getting better.

I suggest trying to join a bike club. Most clubs will have groups riding at different paces. So you can start with a slower paced group and work your way up.

The lighter weight and skinnier tires of a road bike can take some getting used to if you are used to the heavier mountain bikes with their fat tires.

One of the advantages of a road bike is that you have a variety of positions available. You can leave your hands on the tops, sides or drops or a combination. This will help you with soreness.

I guess it was the tension of it being the first time. I was so tensed and also that day I had cried over a bad news. I guess it could have been the tension. I read a good article that covered pretty much the most basic on road biking and it helped. I went for a second ride in an open road where there's no traffic. I felt more comfortable and I will continue to practice.