Can a gyobn get away with telling me I''m not pregnant and then 7 months later I am, is there anything I can do?

In the United States, claims against physicians are based on the tort system, which means that the physician must have done something wrong. A gynecologist is not a guarantor of your health or of your non-pregnant status. While it is possible that you might be able to make some sort of claim, you did to be able to articulate how the physician erred when compared with the community standard. Unless it would be customary for a person in your circumstances to be subjected to a pregnancy test (which would not normally occur unless you reported that you had missed your period), it is unlikely that you could prevail in a lawsuit.