Dear An: Congrats on daughter! Goes to show that we should never say never when it comes to a woman conceiving.
Beginning around age 35 (and you conceived at age 32), commonly there is a slow decline in fertility until actual menopause. You mentioned losing 25 pounds over the past six months--which can be helpful in improving the rate of ovulation frequency. Thus you have both an age related disadvantage and a life style advantage in terms of conceiving again. Any "male factors" (eg sperm morphology) remain unchanged since your last conception. Continuing to work with your OB/GYN is to enhance conception chances is a good choice.
In terms of the current "too light" flow, the first thing to do is to rule out pregnancy if you have been having unprotected sex. Once pregnancy is ruled out there are several POSSIBLE explanations for a "too-light" flow" in a woman not using hormonal forms of birth control:
1. Lowered estrogen levels--this is more likely to be the case in a woman around the time of menopause. This seems less likely given your age and history of regular periods.
2. Elevated prolactin levels---prolactin is produced from the pituitary gland. Levels can be elevated from a benign pituitary adenoma or from certain psychiatric medications. This tends to produce consistent too-light flows--not just a single episode.
3. Missed ovulations--with a missed ovulation the lining of the uterus does not shed all at once. This can result in a missed flow, a too-light flow (just part of the top layer is shed), or even prolonged/erratic flows. This would be the most likely explanation.
IF a missed/late ovulation is the culprit, you are correct lifestyle changes (if perceived by the body as a stressor) can interfere with regular ovulations. Should the too light flows continue or be part of a pattern of erratic bleeding see your OB/GYN for follow up.
Thank you for the inspiring story about your pregnancy.
Yours,
Jane