Hi Madre,
I've done the HG thing twice now, currently on my second round, lucky me.
Before both pregnancies, I was active and fit. Weights and interval work, 2/3x a week, and 2x runs a week, plus one long one at the weekend. I would say I was quite addicted at one point, and would be itching to do a session. I loved the feeling of afterwards.
On my first pregnancy, I didn't expect HG so it knocked me for 6. It was hard getting up from bed etc. When I was around the mid twenty week mark, I started doing preg yoga, which was run by my antenatal clinic. When I was 30 weeks I started going on long walks with my dog. After pregnancy though, I had no problems with getting back to my previous level of fitness, and I would say my fitness level and body were even better than pre pregnancy. So I wouldn't worry about getting back you're previous fitness and strength when it's all over!
I'm now 17/18 weeks now, and have lost a lot of muscle with HG, and my strength is shot to shit tbh, especially the tone in my upper arm muscles, which was hard won believe me! Like you, even though I've lost weight and am thin, I feel flabby and out of shape.
This time round I'm going to start to do resistance work on my upper body when I feel better, as this was the area that was hardest to get back to normal last time, although you may find it different for you.
I would listen to you're body, as HG takes a while to recover from even when you're eating normally again. Maybe get one of those pregnancy yoga or pilates DVDs to build back up, when you feel better. Then graduate onto more. I do sympathise, I see people out running and feel jealous. You will feel normal again though, and back to the gym, it just takes a while.