I would suggest taking poo samples to your vet. There is a lot of resistance to panacur around, so you may find they need worming with a different class, and if going to the vet anyway, you could get them to send it away to check for fluke eggs while you are at it to know exactly what is going on.
Perhaps a friendly local sheep farmer, or your vet could give you an idea of what condition score they are, as anything from BCS 1-4 you will be able to feel the lateral processes, the difference is how much fat is covering them. Knowing exactly what they are at will tell you whether there is a problem.
If you Google body condition scoring in sheep, you should get plenty guides with pictures and descriptions of what you should feel, but nothing beats a hands on demonstration from someone experienced.