Swollen area under my dogs arm

[rowea2]

Over this past week I found a small hard lump on my dogs belly.  I got her into the vet right away and on Monday set up and appointment for this next Monday for surgery to remove and biopsy the lump.  While I was there, I had the doctor give her her annual shots (i.e. distemper/3 year rabies).  For the last two days she has been very distant and having trouble walking and jumping up and down the stairs.  At first I thought she was probably just sore from the shots, but today when I got home from work, she wouldn't get out of bed.  Usually she runs to the door when I get home from work.  I went upstairs and could see that she was having difficulty jumping down from the bed.  And then she wouldn't walk down the stairs.  I starting examing her to see if anything was wrong and I discovered a large soft swollen area under her right front leg.  It is not in the location of her shots and is sore to touch.  She trys bighting at me when I touch it.  

So, my question is, could the swollen area be by chance from the shots.  Or, should I be concerned that it could be something worse?  

Thank you.
Amie

[rowea2]

She is going on 7 this summer and is a Jack Russell terrier.  

[LL7970]

How old is she, and what breed is she?