Gayle, when you start LC it takes your body time to adjust to burning a new fuel. It is advisable to hold off any intense exercise for the first few weeks - then work your way back up slowly to your pre LC levels of intensity.

You might find that keeping carbs below 20g wont work for you if you're working out that hard - you'll end up tired and sluggish. I know that if I let mine go below 40g EC (usually 60g minus about 20g of fiber = 40g effective carbs) I can tell - and it's not pretty

HTH,
Nat