First question: What kind of fish are you getting hits from? The following two questions are about sunfish and bass. I don't know if they pertain to trout.
Second question: Are you SEEING the fish that are hitting?
I ask because of my own experiences, where I CAN'T see the fish. I get strong hits, over and over again, with no hook sets. When I finally DO hook one, it's a 2 inch fish. They hit hard because they're trying to beat the competition and carry away the prize (food).
Third question: Are you feeling "weight" on the line but still not getting a hook set?
This is another situation where "small" fish feel like big fish. I set the hook, only to realize the fish has "come with the hook" rather than sitting still while the hook penetrates. This also happens more frequently with fish that are undersized.
Either of the above situations is more likely in the Spring, when hungry, underweight fish are eagerly grabbing food, and running with it. They don't know to run AWAY from you until the hook set. Before that, they're running from other fish trying to take their prize away, and that can be straight towards you.