Thank you for your query? 
Allow me to explain a few things in order to help you understand better. 
Would you please clarify a few things for me first? 
1)do you have children? How many? 
2)have your periods been regular? 
3)are you on any medications? 
4)have you ever taken birth control pills for more than 6 months at a stretch? 
5)do you have any family history of abnormal uterine bleeding?
A woman's menstrual cycle is regulated by the hormones which are responsible for the development of follicles, it's maturation and release of the egg which may or may not be fertilized. 
 The first half of the menstrual cycle is supported by the developing follicles, by estrogen production,  which enable the proliferation (thickening)  of the endometrium (inner lining of the uterus) to support a possible 
pregnancy.  The second half (after ovulation) is the secretory phase, supported by the 
corpus luteum (through 
progesterone synthesis) which improves and develops the blood supply of the endometrium and prevents uterine contraction. 
If a conception occurs, the progesterone synthesis continues by feedback mechanism from the embryo. In the absence of conception the corpus luteum stops producing progesterone and estrogen starts to rise slowly resulting in a period. 
As a woman ages,  the number of follicles reduce,  there is a small amount of estrogen being produced but no follicles to develop,  no ovulation occurs, no feedback mechanism to shed the endometrium. 
The number of anovulatory cycles increase and bleeding (not a regular period) is basically due to the weight of the endometrium that continues to proliferate under  the influence of uncountered estrogen. 
Normally, this effect of estrogen reduces as its production ceases to attain 
Menopause. 
Sometimes 
hormonal imbalances or extraneous estrogen (food, plastics) that find its way into our system can mimic the estrogen in our body.
This then causes abnormal uterine bleeding and increases the proliferation of the endometrium. An 
ovarian cyst can produce a lot of estrogen which is unopposed due to absence of ovulation and can cause irregular and prolonged bleeding 
An endometrial thickness of more than 10mm should raise concern and be evaluated. D&C to clean and remove the lining is warranted.  The tissue will then be sent for a histology exam to look for any abnormality. 
You may be given medicines to counter the effect of estrogen.  Be sure to discuss all your options with your 
obgyn.. Perimenopausal period varies from woman to woman.  And a conservative approach is the way to go unless otherwise indicated. 
Hope this helps.  Wish you good health. Please get back to us if you  need any clarification