Deworming sheeps

How many sheep do you have?
I think they need more pen space. Like, a LOT more space. Rotating them from paddock to paddock would help keep the worm load down. Wormer type depends on the type of parasites found.

I have not heard of non pharmaceutical cure, other than Sericea lespedeza (I think that is right). https://www.wormx.info/slcoccidia

I think you need to find out what parasite. and hit them hard with multiple dewormers over a short period to knock it back, and then get a regular deworming program in place.

I am not opposed to an organic approach but where warranted a modern med can be your only choice for the animals sake. Condition will gauge your time line. If they have lost condition fast you must act quickly to stop that loss with ivomec or a safeguard type wormer. I lean towards a safeguard type. If that was not your plan start over with more resistant sheep and improved conditions.

you could take your sheep fishing they will use up all their worms as bait.

Garlic, tobacco, pumpkin seeds, cinnamon, and (DE)are a few of the mythical wormers. None of them work at all ever.

I worm my herd 3 X a yr. I worm ewes when I turn the buck in ,then when they lamb with clear wormer ( Iveomec) and then again when grass is good and when I wean lambs with Valbazen.