period lasting 4 weeks

Hi,

I have a question regarding my period. I have very unusually had a period which has continued for 4 weeks. I have a period every month which lasts for 5 - 6 days thats been the situation since a teenager. I am on no birth control and have not taken any pill for 15 or more years. I have 3 children youngest is 6 years old. Never had any issue with getting pregnant. I am having mild cramps but not that often maybe a few each week since this 4 week period. Might I be pregnant? well I certainly dont feel pregnant, I could be but I dont feel as though I am. I havent been to the doctor as I was rather hoping my period would have gone by now. I have never bled for this long the longest I have bled for is just after a baby and that was only for a week to 10 days if I remember correctly. Please advise as to why I am experiencing this.
My breasts are tender but they always are during a period. I havent changed my diet, I am a fit 5 foot 7 inch female who weighs 9 stone, size 10.... I dont smoke - very anti, hate it, and I have a few glasses of wine per week. I dont really do any exercising but am always gardening cleaning running around with the kids etc. I consider myself fit as I dont get out of breath and in the summer months usually enjoy swimming water skiing and pretty active pastimes.

Please advise

Thanks in advance