Need help/advice

5'10" F Age 67 SW 228 CW 218 I have been on Keto since Oct 15th. Weigh and measure food carefully. 1500 cal/day 20g carbs or less/day Eating window 1 p.m. - 6 p.m. My problem is the 3 week stall. Also, overnight my ketosticks went to negative. (I know some say to ignore the sticks, but the sudden change plus the stall give me question.) What foods may trigger this? I eat pretty much the same thing every day. 2 Eggs 1 sausage patty, 4 oz chicken or turkey or ground beef. Coffee, HWC and 8 oz bag of mixed greens (salad) with full fat Ranch. I am not hungry, seldom snack but if I do it is 2 garlic stuffed olives or 1/4 C pecans or 100 cal avacado cup I do add cheddar or mozzarella cheese to either my eggs or salad. Fought off a horrid cold. The cough syrup I had on hand had 9 carbs!!!! (Looked it up later.) I know that ruined at least 4 days, but I'm still stuck. Any suggestions? More water? Missing anything? My first post. Sorry for the length.