I'm 105 pounds and used to have my period for 3 weeks on and 2 weeks off and that was my cycle. I am now extremely anaemic because of it and have several other health problems due to it. My gyno gave me no option but to go on birth control and only have my period 3-4 times a year because my body can't handle menstration. You should probably do the same and get a different doctor because he is an idiot. You should not have to go through that.
You're bleeding too much too fast. Anything less than two hours to fill a pad or tampon. It could be hormones, could be weight, could be anything, but you'll want to find a doctor who will run tests to be certain. If anything, you can try instituting a fitness regiment and exercising portion control in case it really is just the weight issue. And at the very least, you need to be monitored for anemia.
I'm obese and my period won't be for more than 5 days, very heavy, but that's because I have fibroids