Have finally got positive testing after sooooo many negatives. Looks to me like what I had tested as being white blood cells, contained in mucous and discoloured due to where it came from :)
If yours is the same, I am almost certain it is the result of a liver flukey type parasite which is very difficult to detect. I had the same issue, very rapid weight loss over a short period and then maintenance of the same weight thereafter. Waiting to see if Triclabendazole (which is very difficult to obtain here) effectively deals with the issue.