My Dog has a lump on his back and he is only 1yrs old what can it be?

I noticed that my Doggie had this little lump yesterday... and it wasn't that big or swollen I should say. Today I noticed that it got a little bigger and it is swollen but my dog doesn't seem to find it disturbing him at all.. I am going to take him to the Vet the only thing is that both my boyfriend and I don't have money right now because I still haven't been able to find a job, and until this Friday that we get some money I will be able to take him in. can anyone help me and let me know if it is something to be very concern about?