Small bump on top lip

Since Tuesday (Feb 23) I have noticed a small bump on the edge of my top lip. It is not on completely on the outside or the inside of my mouth, but in between. If I put my lips together you can not see it or feel it. The bump seems to have the same shape as a pimple, but there is not head on it. If you look at it closely you can see it pulse and I can feel it pulse if I put my tongue on it. There is no pain, itching or irritation. It is the strangest thing! It seems to go down at times, but then be the regular size at other times. It is not getting any bigger though. I am 26 years old and was a half a pack smoker up until about January, then I cut down to 2 or 3 a day and since the end of February I have been down to one a day, if that. I just wondered if anyone knew what this could be?