Patches on tongue...not thrush

My 4 month old baby has these patches on his tongue that have been there for about a month now. They don't seem to bother him and they go away and come back in different places on the tongue, but there is always at least one there. All the info I can find about patches on the tongue are about thrush, but I've read the description and thrush doesn't seem to fit what my baby has.  They aren't white and they don't appear on the insides of his cheeks.  They look like suction cups. Does anyone have any ideas?