I work at a veterinary office, ours has a boarding facility, which I worked in for 2 years at the beginning. Some dog bark, and play hard, & some you can tell are stressed from being away from there family, leaving them very lethargic when they go home. There are some things I would recommend for your next trip to boarding.
1) Get your dog vaccinated for K-9 Influenza (H3N8). Bordetella / Kennel Cough is like a upper respiratory infection while K-9 Influenza is truly like the common cold for dogs. We usually give this to dogs who frequent dog shows or are prone to getting sick around other dogs (which yours sound to be). I do it to my dog for peace of mind, she comes to work with me daily and stays in boarding while i work. It is a vaccine given once, then repeated in 3-4 weeks, then booster yearly.
2) Bring toys & a blanket/ towel that smells like you to minimize there stress. (label them well so they don't get lost)
3) Ask for a walk, one-on-one play time, brush, or massage for your dog daily so they feel less lonely while boarding. It usually is an additional fee (~$5-$10) but well worth it, if it saves you a trip to the vet.
Hope this helps.