Whats wrong with my dogs breathing?

Everytime my dog runs with the other dogs it pants really hard after its done and has what I call an "asthma attack" It hacks up flem and is all out of breath. It sits down and does nothing until it calms down. She is only 7 months old and is mental i didnt know if that had to do with it or not. Also her name is Boo Boo the Jack Russell/Chihuahua mix! Thanks for all the help. Yes, She will be going to the vet soon! I just want a guess, i think its dog asthma, what about you guys?