Depends sa pag toothbrush. I'm sure you're using age appropriate brushes approved by your pedia. Also, it may be the toothpaste acting as an irritant. When my son was less than 18 months old (before he learned how to spit his water) we used SansFlo toothpaste (Mercury Drug) Flouride free. Aside from swallowing flouride, which is not a good thing, residual chemicals may affect your baby's mouth.
My dentist however, recommended that I use no toothpaste until after a year. That, hindi ko ginawa. Makes sense, pero yung yuck factor for me nan doon.
So what I do is I use a very minimal amount of toothpaste and make sure his mouth is rinsed well. He's a year 10 months now, and the toothbrush we use is Oral B.
It's all a little costly, but sulit talaga sa pera and the best thing is we make sure our children get the best.
A singaw is minor, but kung tayo naiirita at minsan di pa makakain, ano pa sila.
Best regards to you and your family!