Hi there

I am looking for some advice. First thing to say is I am booked in to see my dentist however I am working myself up worrying so hoping someone could help with any advice. I am also very dental phobic, which doesn't help!

I have noticed a lump on my gum, above my molar tooth. The bump is painless and seems to come and go. When it appears it is firm and less than the size of a pea. If i push down on it, it does go down and also goes away on its own after about half an hour after is appears. It has been there around 4 weeks now and I have no other symptoms. 

There is no puss or redness/discoloration and no unusual texture. It is under the gum and when it goes down again it feels completely flat and back to normal. I am worried sick that this could be a cancerous lump, although I am not sure if a cancerous lump would come and go the way this does. Somedays, it isn't there at all. It seems to appear when I rub my tongue over the area (which I know could be irritating my gum :(

I am 37 and an ex smoker. 

any opinions would be most appreciated.

Thanks :)