Why do I feel itchy when I go into these clothes?

I work at a childrens clothing resale shop, and while pregnant about a year ago they let me take home a lot of the donations because i was young & needed the help. The younger stuff ive washed a couple of times by now but it was itchy & had a smell, like a good or nice smell gone wrong ( Best explanation I can think of.. it's pretty hard to point) when i got it. I am going through the older stuff as she gets older, & its still really itchy, & still has the oddest smell that cannot be explained. & this time i felt a grain of sand on me, picked it up & i swear it jumped.. i tried to mush it but it feels & looks like a grain of sand with a liiiiitle black in the middle. Same size & feel as sand on the beach. That's what it couldve been, but im exploring every possibility. I cant find any answers & i was wondering if anyone had any idea of what possibly could be going on.. thank you.