Keep at it, and also be aware of the angle of your hookset. Depending on how the bass took the frog will depend on how you set the hook. Now if your night fishing, then I agree its a feel thing. However during the day, observe the frog and when a bass blows up on it wait to see if the frog is gone and then swing for the fence. If a bass just slurps the frog like an oyster, observe that it indeed took the frog and then set the hook.