yawning and not flicking tongue are early signs of an RI. they are not definite but it should cause you to pay attention. check its mouth for excessive mucus. check the tub and everything for mucus streaks from rubbing its face on stuff to get rid of mucus. check water bowl for an floaters. sometimes u can here pops and clicks when ur snake breathes if you hold it to ur ear.
if you suspect an RI go to the ASAP and get a Culture done to test for the correct antibiotic. injections are gonna be given so if your not confortable doing it ask your vet to teach u or if you are close enough you can go every 3 days and they will do it. its very easy to do. ive never had Oral Meds that work goos so if they prescribe it ask them to give you injections.
Many factors can cause an RI so even if your husbandry is right your snake can still get sick.