Should the dentist have handled this differently?

Last March I had a crown put on a cracked molar and since when I have seen my dentist I complained about varrying levels of sensitivity in the tooth. At my cleaning in September I complained of the same sensitivity (cold, when I bite, and sometimes just pain). He looked at the tooth and the x-rays and told me I did not need a root canal. A few weeks ago I had an appointment to put on permanent crowns on my front teeth (I had a temp. crown on). The front teeth were originally broken as a teenager and bonded, at my dentists urging I decided to have them crowned. At this appointment again I complained about the pain in my molar which seemed to be getting worse. The front crowns were fitted but were too long and had to be sent back to the lab. Tonight I had another appointment to cement the front crowns. As soon as I went in I complained about my molar. The hygenist asked me about it and x-rayed it and said we would talk to the dentist about it. When the dentist came in I told him the problem and he said that I would need a root canal. They then cemented my front crowns. I went to schedule my appointment for a root canal and I was told that the cementing of the crowns used up almost all of my insurance and the root canal would cost me $600 out of pocket, whcih I cannot afford. I am very frustrated that my dentist chose to cement these crowns and use up my insurance when I had another problem that was causing me pain. I have never dealt with a situation like this before and am unsure about how I should proceed. Any suggestions? Do I have a legitimate complaint or do these things happen? I'm not sure if it matters, but I have very good dental insurance and I am double covered (by my own employers insurance and my wife's). Thanks!
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Sometime it is the case that a patient could be feeling something and nothing shows on the xray, so it is possible that there was nothing there to see. But what troubles me is that he didn't do anything to try and deal with the sensitivity, like put something on the tooth for sensitivity or since you told him that it was getting worse, wait a while on cementing the crowns to see if you were going to have a problem. The thing is though about the insurance is that it is not the responsibility of the dentist to really worry about your insurance. The insurance is a policy is between you and the insurance company, so dentists don't think about treatment or possible treatment in terms of what fits into the realm of your policy limits, you as the patient have to make sure that they do, by letting them know that you need to work within those guidelines, and in most cases remind them on multiple occasions. They really only think in terms of fixing any teeth that need to be fixed... "One track minds" :)
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