I walked the Frances twice, and portions of the VDLP, the Aragones, and the Norte.
I was only bitten once, at the beginning of my first Camino, in Zubiri.
I didn't know what the huge painless welt was until much later.
Since then, I've followed the advice of a pharmacist in Spain and have never gotten a bite.
When you arrive in Spain go to the the first Farmacia you see and purchase mosquito spray.
This is the spray you are supposed to put on YOURSELF --- but don't do it.
Instead, follow these steps:
When you first get to the albergue, do a check by eye to see if you see traces of bedbugs.
Those include little tiny specks on the walls near the bed or ON the bedframe. They look like someone took a black inkpen and just tap tap tapped the wall. That is bedbug poop. If you see that, then I would not stay there.
Next, check the mattress all around the rolled seam. This is where the bugs like to hide. If you see bugs, leave.
Next, on the bunks, there are holes where the hardware connects to each other. Check those holes with a flashlight. If you see bugs, leave.
Lastly.. if you have checked all these things and are convinced there are no bugs here, then take out your mosquito spray and LIGHTLY spray the bed... 2 or 3 pumps about a foot above so you're just lightly misting it.
Then WAIT 5 minutes.
If there are bugs, they will come out to escape the spray... If you see them, LEAVE.
Some people on this forum have said not to spray - but I have chemical sensitivities and I can tell you that the tiny amount of this sprayed on a bed in the early afternoon dissipates completely before bedtime. The sheet you speak of gives me a migraine, but the spray does not.
Anyway.. this is my advice.
I have done it for 6 months with only one bedbug bite before I knew about the procedure.
There were a couple of times when I took a taxi to the next village. There's no law that says you cannot do that.
There are a lot of articles and photos online to see what bedbugs and their signs look like.
Study those too -
Buen Camino!