Weight issues :(

I keep losing weight. I've been to the doctor and had blood work and everything seems normal. I had this issue about 6m ago and went on a supplement that was supposed to help me gain and although It didn't help me gain any it did help me maintain my weight level. Now I'm dropping again, my pre-pregnancy weight was 155. Then I dropped down to 140 and this morning on the scale I was 129 😬. Could stress do this? Has anyone experienced or know someone who experienced something like this?