I have fish allergies. Does this mean that I am also allergic to frogs?

Unlikely. Although i can't say this for certain, I am not aware of any case reports or studies showing any cross-reacitivity between fish allergy and frogs. In fact, I have never heard of an allergy to frogs. On the other hand, frog is not a very common food, so allergy to it may be unrecognized. You should discuss your symptoms with your primary care physician or allergist.
No. An allergy to fish may not be to all fish. Since frogs are very different than fish, they have many different proteins. It is perfectly possible that you will not be allergic to both fish and frogs because of a common allergen. But, you could be allergic to one thing in fish and another in frogs, for example.