Well...you usually are looking at about 60 days for pregnancy so pups should be about another month away. If you have a rectal thermometer it wouldn't be a bad idea to check her temp. (Normal temp 101.5 degrees - dogs' going into labor usually drops to about 90 degrees). Panting, if not obviously overheated, can mean signs of stress or discomfort. She's in the middle of her pregancy and at the time when the growth of the pups can be seen or felt - possibly she is feeling the natural discomfort of carrying pups. I would be concerned and seek a vet right away if she has discharge or bleeding, signs of infection, stops eating/drinking, and/or becomes very lethargic. Would there be any other factors for her to be stressed or uncomfortable tonight? Active weekend? Did she eat anything different? Some things for you to think about. I would keep an eye on her tonight and see how she progresses. If you have further questions or concerns let us know.
Please reply to any questions or let me know if you need further assistance!Otherwise, I hope you have found this answer satsifactory and worth acceptance!
Oliver's Mom