Hi Steph55
Yes, female hogs do tend to make their nests near to the time of giving birth. But there is usually a fair amount of nest building activity, often early in the morning. Although, males will take small amounts of material into nest boxes which they sleep in too. So it depends how much nesting activity you were seeing.
Sorry, I could only surmise as to why a hog would be going in and out of a house like that. Sadly not all hoglets born make it out into the world (it is one of the most difficult times of a hog’s life), but fingers crossed, if there were indeed hoglets in the hog house, you will be seeing them now. Hoglets are big enough for foraging trips with Mother hog at 3 or 4 weeks old, so if there were hoglets they should be venturing out by now. It’s a few days since your post – maybe you’ve seen something since?
Let us know if there are any developments. Good luck.