active mommies?

Any ladies like me who are usually at the gym, running or lifting? I'm just now starting to feel like tired at 6 weeks but my muscles get exhausted really quickly it seems. This is my 3rd and I'm trying so hard to stay fit. I gained a lot with the last 2 (not too much but I didn't feel good) I want to "bounce back" easier this time. I don't want to take a year to be back to my normal body.