concerns about 8 month old dog

Question
I just returned from a 10 day trip to Minnesota with my 8 month old dog.  Since returning home, he has vomited once per day - but is still eating, drinking water and going to the bathroom normally.  He is also very sleepy and isn't his usual self.  Should I be concerned?  While on vacation, he did eat some of my sister's dogs food.  Could this be causing the vomiting?  When he vomits, its watery with no food.
I currently live in Sonoma, Ca and the temperature has been over 100 for the last 3 days.  Could this be any of the problem?

Answer
Rebecca -

If the weather is extremely warm, then please leave your pet in the house during the day.  Dogs do not sweat like we do and it is difficult for them to fend off the effects of extreme heat. Have your pet evaluated by your veterinarian to determine why he is vomiting.  It is almost impossible for me to determine why he is vomiting without examining him. A thorough exam will help determine why he is vomiting and treatment will help him to feel better.

Best Regards,

Charlotte Sherrell, DVM