Yes it can be bad to eat too many clams.
When you eat too many clams you increase your selenium intake which can be bad for you.
When you consume too much selenium it can cause hair loss, nerve damage, irritability and even nausea.
So you want to watch how many clams you consume or eat and it's best to not eat clams everyday or every other day.
Eating clams a few times a week should cause no harm but eating too many clams may cause you to become sick or ill.
However if you're not experiencing any of the above symptoms then you're likely fine with eating the amount of clams that you're eating.