You can have her titered and see if she is already immune. It is a blood test that checks for antibodies. I had Deja's done at 4 years and she was strong for Distemper and Parvo after only her puppy shots. I have only given vaccines for two diseases: Parvo and Distemper as single vaccines only two weeks apart from each other so per vaccine/disease that has been 4 weeks apart. I think you'd be fine when you give your pup another 3 weeks from the last one. But do take him out in the world to safe areas and don't let him sniff in grass and on urine or feces.