As the title says really. Just loaded my save to carry on playing and looked on the reputation tab. Only Goodsprings and Novac are there. Is this a bug or am I missing something obvious?

I too am having bugs like this. Random times I check my Reputation in my PipBoy, it doesn't show all the factions, sometimes it'll show 5. Sometimes it'll show a full page, but still missing a few factions. There should be at least a dozen there.

I've found wearing faction clothing often causes this, try putting one on then taking it off.