irregular periods and Keto

I have been on Keto for 4 weeks now. In the first week I lost 12 pounds which seemed like A LOT so soon (I'm 5f4" and started at 154 pounds). However I know a lot of this was likely water weight. Halfway through week two I started spotting and then bleeding like a period even though I was only a week into my pill packet. I've done some research and have seen that some people have these symptoms and it is "normal" on the Keto diet. I would love to know if anyone else has experienced this and if it stopped? I don't fancy being on a constant period :( I also have an Underactive thyroid which is a result of post partum thyroiditis that became permanent Underactive thyroid after a year. I've heard that people with an Underactive thyroid shouldn't do Keto as it can make it worse but I'm finding I have a lot more energy than before so surely it can't be making it worse? I really don't want to stop now because I've lost 15 pounds so far and feel great!I plan on going to the doctor next week to discuss the diet and how it's affecting my periods and also to see if it has had any affect on my thyroid. I would just love to hear some personal experiences of this or some advise before my doctors appointment.