It has been a few years now. but I still remember the first couple of weeks after surgery. Before surgery I was a gym rat, working out and jogging 5 days a week, not overweight, non-smoker -- you get the picture. I tried to do it right. Immediately after surgery, I was "weak as a kitten" for several weeks. I could "operate" my body to get around the house, but stairs were slow and tiring. I was so weak that I remember when I took my first walk outdoors after surgery, I had to stop and catch my breath at the corner before I could walk back home (1/2 block).
For me, I felt bad for most of the first month. After that I got better more quickly. I wasn't ready for cardiac rehab until 3 months out, but after that I quickly got back to almost normal. Even after the first year, I was still seeing improvement, and now even though I am 4 1/2 years older, I feel better than I did prior to surgery.
By all means, if you feel badly get to the doc for verification that all is well. In the beginning, many of us lose confidence in our bodies and need the re-assurance of our doctors that things are OK and will continue to heal. Also, remember that we all heal at different rates. Some folks are back on their bikes and running at 3 months, others of us take longer to get back to it. But also remember that almost all of us end up in better health than before surgery. That's why we do it.