Use this phrase to talk about something that you have to do all the time.

Having kids isn't easy. You constantly have to chase after them.

You'll also hear people use the word "constantly" after "to":

I had to constantly check up on them to make sure that they weren't messing it up.

The word "constantly" means without stopping, and without any breaks. However, people are sometimes exaggerating when they use the word "constantly".