Question- how low carb was the low carb... like Atkins low carb (hardly any) or more balanced, like South Beach?
If it was Atkins.. many people actually gain back 4-5 pounds immediately after introducing carbs. I forget the scientific reason, but it has something to do with water being stored in the liver which you lose initially (and gain back immediately).
If you have not excerised before, I would lower it down and start milder, focus on weight bearing... like 20 minute sessions total at first. I would also avoid the highly processed carbs (i.e. sugar, white bread) until your body gets used to it.
Everybody's body is different, but back when I actually had time to exercise / prepare food / eat healthy, when I cut my calories too much (this INCLUDED exercising much more than I was used to and keeping calories the same) I lost NO weight - my body thought it was starving. I had to increase calories by a few hundred until I started losing (or lower exercise).
Also, watch the salt. A lot of carbs have high salt content, and (also if you are excercising a lot more and not increasing water) your body could be retaining onto fluid.
I wish I could take my own advice and have time to exercise or prepare food/eat well