Hi A., I would simply tell you not to worry about it, and don't compare him to you. He's much less likely to have comparable issues as he's done with passy at 2-1/2, whereas you sucked your thumb till 6YO. And thumb sucking is probably worse because it's more likely a constant, whereas passy becomes just a bedtime/naptime thing at some point.
So, don't worry... get him to the dentist, have a assessment, and be totally informed of what your family may (or may not) be faced with. You'll feel so much better afterwards, and can begin dealing with it.
And always remind yourself that it could be so much worse... cancer, leukemia, disabilities, lazy eye (my daughter began wearing glasses at 20 mos.!!), bedwetting, etc. We as parents just have to deal with it, and help your child overcome. Good luck to you and your family!!