Irregular period or what? Help!

Okay so the deal is I get irregular periods, I'm used to them never really being on time but I have a little window of time each month that it comes. Usually between the 4th and the 8th. In August is came on the 14th, but it wasn't a sure period it was rather light and barely red mostly brown and lasted like 5 days. Then yet again the 31st I started spotting and I have been spitting since then, so about 3 days now and I called my obgyn to see if I needed the appointment and the lady I spoke to said it sounds like I'm pregnant. I also spoke to a nurse however she said she thinks I'm not. She thinks I'm having an irregular period again. I have an appointment in two weeks but I would like to know what you ladies think! I'd appreciate all the advice I can get! I also took a pregnancy test yesterday and it came up negative.