Hello,
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I have read your query and understand your concern. At the age of 17, you need not worry much about the changes in periods. The period cycle is 28 days +or- 7 days is fine, the duration of periods up to seven days is also fine. But the real problem here is your weight. From your history, I presume you have PCOS ( Polycystic ovarian syndrome. This is a congenital condition, I mean it is a genetically programmed condition, you get it from your parents. When you suddenly put on weight, this cholesterol is converted into estrogen hormone (if I may simulate- haven't you seen obese men developing breasts and in young obese girls, who develop periods at a younger age, they all have high levels of estrogen hormone or female hormone). In your body too, when fat, which is a store for tomorrow, is more than normal, this is converted to a hormone that tips the balance between FSH (from the brain ) and the ovarian hormone. FSH (follicle-stimulating hormone) as the name suggests stimulates the follicle from the ovary, but once the follicle is big enough to ovulate, the FSH is suppressed by the same estrogen hormone from the ovary. But when the same estrogen hormone is coming from fat, the brain is confused and follicle growth stops early at a smaller follicle size and will not rupture, next scan you will see all these follicles as polycystic ovaries. This is usually associated with obesity, irregular cycles, no periods for a few months, and later heavy periods with clots and fleshy masses, spotting on and off, thyroid abnormality, and prolactin problems indirectly.
You develop that extra pad of fat around the mid-segment of the body, especially the waist, thighs, and breasts, with no fat beyond the elbow and knees. Excessive body hair growth, hair fall, a dark shade over the lower half of the face, acne, oily facial skin, black skin over the back of the neck, inner thighs, and under the surface of the breast. May have a family history of diabetes, especially father or his family. This will not allow ovulation to occur at a time so you cannot get pregnant, till treated. It also increases your chances of early pregnancy abortions. But this has a solution. Your weight has to be
Weight(in Kgs) = Height (in cms)-100. Your expected weight is 114 to 125 pounds. Once you reduce weight to the normal range, you will not need any medicine to get periods or to get pregnant and pregnancy will be healthy.
To reduce weight - Avoid fasting, junk food or fast foods, and red meat, and reduce snacks in between meals. Have low-calorie food and high proteins. Regular exercise (especially for the waist and hip area), aerobics, yoga, brisk walking (swing your hands well), try to reduce two to four kgs in a month. Do not hurry on weight reduction, it will be difficult to maintain. As soon as you reduce at least five kgs, you will see changes. By having the birth control pills, you will be creating an artificial hormonal balance in your body and getting periods, but the underlying cause for this irregularity is fat, so treat the cause and not the symptom. These changes in periods are an indication for you to react and try to shed those extra pads of fat.
Hope I have been of help to you. Thank you.