I've experienced a similar problem yet instead of Doc Mitchel's house it was a series of caves in the upper North-East part of the map.
First step is to backup Fallout:New Vegas ini files which can be found in \My Games\FalloutNV <== very important to do so you don't lose any settings for the game or any mod you've installed.
Second Step is to verify game cash through Steam. Right-click on Fallout: New Vegas ==> Properties ==> Click on the Local Files Tab ==> Click on Verify Integrity of Game Cache... button.
Let Steam do it's thing and when it is done it may or may not say that "x number of files failed to validate and will be re-acquired."
Once it is done re-acquiring the files then copy your ini files back into \My Games\FalloutNV.
Go back into FO:NV and see if it worked.
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