Dear Lylan: The initial irregular periods (before pregnancy) were most likely the result of occasional missed ovulations. You mentioned that postpartum periods were regular until your daughter was a year of age. At that time you were put on hormonal birth control (?birth control pills). Since large fibroids were ruled out by ultrasound the most common explanation for the current abnormal bleeding is breakthrough bleeding (BTB) on hormonal birth control.
Alas, breakthrough bleeding (BTB) can be a common side effect of most types of hormonal birth control (eg pills/patch/ring/shot/Mirena IUD). Among birth control pill users BTB frequently occurs after a missed or late pill. In your case it sounds like you are careful to take pills at the same time daily. More remotely, BTB in a pill user can arise if she has gotten a chlamydia infection. Yet, if you both are monogamous this is not going to apply.
When a woman uses hormonal birth control it can make the lining of the uterus more unstable--so it is easier to have some of it begin to shed. Sometimes the lining is less stable because the hormones make the lining much thinner (actually this is good as a thin lining is a healthy lining). Yet in a longer term user (eg you) the super thin lining can be less stable and begin to have prolonged or erratic bleeding. Sometimes the lining is unstable because the hormones can make parts of the lining out of synch. This is more common in brand new users. In your specific case the initial month of use that produced such a heavy flow following a time of no flow is an example of this scenario.
You did the right thing in ruling out fibroids since you have a known family history. It may be that fibroids will develop later. If that occurs you still have options other than hysterectomy.
In terms of a trigger for your current BTB it MIGHT be that stress is the culprit. While the mechanism for stress caused BTB is well known in non-birth control pill users, there are no published studies linking stress to BTB in Pill users. This is amazing as we get letters every month from Pill users who swear that life stress corresponded to the onset of their BTB. It sounds like you have a lot to deal with as a "single mom" of a three year old. It's got to be hard to have him away so much.
Bottom line, BTB on hormonal methods of birth control is a nuisance side effect. The protection from pregnancy is still in effect. If your poor cycle control persists you should return to your GYN or clinic. Often a change in the brand, or formula, of birth control pill will fix the problem. They can also investigate if other contributing factors are suspected.
In Support,
Jane