breakthrough bleeding and chunks of tissue

I take the pill continuously (without the placebo) because my periods were so bad. I am 42 and wish I didn't have to deal with this annoying cycle anymore. I have always had bad periods my whole life. The pill has calmed them down in order to lead a normal life. However, I get some breakthrough bleeding on this continuous use of the pill still. My doctor told me to allow a period to flow and stop taking the pill for the week. Well, I did and on the fourth day I thought I would die. The red rubbery tissue were so huge and the flow was so much I had to take the pill right away. I was able to stop it after taking four pills at once. I don't understand this because I thought the pill stopped the release of an egg and the build up of the uterine lining. I lost a day of work, my insanity and a pair of jeans.