Will my dog be ok after eating clams?

We steamed oysters for New Year that had an unusual amount of those little clams on them. A lot of them missed the "shucking table" and hit the ground. My pom kept eating them. This morning he was very lethargic, would take a few steps and lie right back down and his stomach is pretty tight. We had to leave the house for a several hours. When we got back he was a little more perky. I cannot help but to continue to be concerned. I tried to find an answer for this earlier - nothing. Does anyone know if this clams can cause damage to a dog and if there is anything I could give him or do for him? Thank You