It's as easy as 1, 2, 3, 4 ...
It's your money and your future .. most of all, agents work for you - not the other way around.
1.) list the situations, all of the times and why you're not happy.
2.) call and make an appointment with the broker/manager
3.) sit down, explain it and get a written letter of immediate cancellation of your current contract.
4.) find yourself a quality realtor from a different office, or go FSBO...
-- end of story.
Not knowing what state you are in makes it difficult. Each state governs the real estate laws for their respective areas. While they are very similar they can have differences. I would suggest speaking to your realtor's Broker-in-charge. You should be able to terminate the contract at will. Although if you go back and buy a home that the realtor has shown you this might make you liable for their commission. So with that in mind Jim has a point in that you should take your buyers agency agreement and have a lawyer look at it. Most agreements will have a period of time after the contract has expired or was terminated in which if you buy a home they showed you then you will still owe the commission.
Hope this helps.
Before you hire an attorney, you should ask your agent to get her broker to release you from the buyer's agency agreement. The broker will likely want to set you up with another of the agents in the brokerage. In all likelihood, the agent assigned will be among the broker's better, more experienced agents.