Reason for frequent sneezing inside the house?

I recently moved to one of my friend's house in San Jose, CA. From the time i got here, i have been frequently sneezing and dealing with runny nose all the time. The interesting thing is, I am totally fine when i go outside. Is it because i m allergic to something in the house (may be the carpet) or is it dust allergy or is it a mental thing ? i m not sure if i should do take any pills or shift to different house .. suggestions are greatly appreciated .. thanks :)