Suggestions on testing radon in small room

I don’t know anything about radon, but I’m curious about it after having dealt with a strange odor that appeared only in my room by the door frame that made me sick whenever I smelled it.

I keep the windows open most of the time, and suddenly after months of smelling it, it no longer appears.

So radon came across me, and I want to test the rooms air quality. Does this mean I would need to keep my window closed for 90+ days to get a clear read on the radon levels? Could I use air purifiers during that time? Air quality has been important to me and I can’t imagine keeping this room shut for 90+ days. It gets stuffy in there quick.

What’s your suggestion?