How Long Does Marijuana Stay In The Body?

Hello, I was asked to complete a drug test last week. Over the last 9 years I've been a pretty heavy marijuana smoker, consuming about a gram a day. I have not smoked in about a month, and my urine still tested positive for THC. I am 5ft and 100lbs. I do not exercise and have extremely unhealthy eating habits compiled mostly of fast food and soda. My doctor just started running some tests on my thyroid, but aside from that I have no other health problems. Do you know how/why thc is still testing positive and how much longer I may test positive for?