I have been on atkins (phase 1 less than 20 carbs/day) for 5 days. I feel like I am starving...?

I am extremely weak and have no energy. I've tried counting calories before, but it didn't seem to work. While cutting calories I was running and working out 4 days/week. On Atkins I hardly have enough energy to walk up a flight of stairs and def none to work out. Please help! I'm 5'1 140 lbs and gained weight when I had my 2 yr old (can't seem to lose it).