Sheltie limping and lethargic

Question
Our 3-year old Sheltie Ruby often limps, bears no weight on her paw, and becomes lethargic, not eating or drinking.  This happens often, and then she'll be fine again.  She can even jump up and chase the UPS man and then is back off her feet again.  We haven't taken her to a vet, as she gets better..... but maybe it's time.

Answer
Jan,

3year old?  "maybe it's time"??  Whaaat??  STOP. Take her to the vet now- I mean today, Sunday, now.  Get her tested for tick diseases, arthritis and whatever else the vet can think of.  Check her tummy to see if it is sore to the touch.  She is sick and needs to be treated.  She should be spry and bouncy for at least another 7 years or longer!

Dave