Too much sex can be a problem when you are trying to conceive (TTC) because it may lower his sperm count. Too much sex when trying to conceive is defined when you have sex more than once a day.
In general, there is no real situation when you can have "too much sex" if both partners enjoy it. However, when TTC, too much sex can harm your chances getting pregnant. If his sperm are OK, then you will probably increase your chance of getting pregnant by making love once a day. Making love more than once a day, however, may decrease the number of sperm, even in men with a normal sperm count. Making love every other day is suggested if he has a lower-than-average sperm count.