Any ideas as to what these are?

my horse was on pasture turnout so when i couldn't make it out to put him blanket on he was exposed to the rain. he's in the stall now. but he has these three bumps, all confined to the saddle area. they are bigger than pea sized, but smaller than a quarter, and firm. he only has three and no more have come. he has had them for three-four weeks. i completely cleaned and disinfected everything. but they are still there. any ideas as to what they are? i was thinking rain rot, because initially they can be hard. oh yeah i did get a new saddle, but it fits better on him than the older one, as checked by someone who knows what they are doing. thanks for the help :)