A good agent will give you a rough timeline for the return of feedback. After all, you can't move forward with *your work* or even make plans as to when you will make time for such if the agent has left this open ended. If for some reason they can't meet the time they set, they'll make contact. That's the mark of a professional.
Some individuals (agents or others) are poor at time management and estimates. You get to know this after interacting with them for a while. Your agent is new to you, so you don't know and neither do we, because we don't know your agent, either.
Three months is long, but if your novel is long and your agent does meticulously detailed line edits in addition to developmental suggestions and they have loads of other clients they do the same for, then three months is not out of bounds.
Echoing kaperton above, I hope you have your answer by now. I've only ever worked with very prompt agents, but I have heard from writing friends some frustrating stories.
