Yes? It really depends on the agents you are talking about because the norms of responding or not responding vary a lot from agent to agent. There are no guaranteed ways to know what's going on with your query at a particular agency until you receive a response BUT if you have the money QueryTracker has some tools which might help. Specifically, you can see when people report sending in their queries and when they report getting a response (you can also get this through the BR&BC section of the forums here and through comments on individual agent's pages on QueryTracker, but that requires more wading), and this can give you an idea as to whether the agents you've submitted to take (on average) 4 weeks, 3 months, or never respond at all.

When querying, I found it best to just assume my queries were sent into the void and continue to send out more regularly. Anyway, best of luck with the (draining, sometimes demoralizing, sometimes exciting) process.