Suggest Remedy For Irregular Menstruation

Hello my name Is shannon and I would appreciate if you would offer my some advice. I have really irregular periods which can vary from 26 to 42 days but they usually come on the 34th day and are always heavy and can last around 6 to 7 days till I m off, they also start off brown for about a hour and then go heavy red till last few days which go brown. I have been in a relationship for nearly 3 years now sexually and haven t ever used protection so I have started to worry if I may not be able to have children. This month I have come on on day 26 and really light brown, have been on for six days and its been brown blood with a tiny hint of red and a pinky colour. I m basically saying I think I may be pregnant, I ve never had anything like this before and have done a pregnancy test which says I m not pregnant. Have also been doctors and spoke to a individual who was really rude and looked down on me as I m 19 nearly 20 and I did a pregnancy test again which was negative. I just would like to have a rough idea as to what may be going on, please can u give me some advice