I've been here since February this year. I need to go back to the US for about a week. When I return, can I convert my US license to a Philippine license?

If I were you, I'd do it before leaving. On a tourist visa you have to be in the country for 2 months, and you should get an extension of 2 to 3 months too.

I didn't convert mine. I just got a new Philippine driver's license.

Something to discuss: when a foreigner gets pulled over by the local police, how would the police know they've been in the Philippines for more than 90 days (if they aren't carrying their passport)?