When you did the fecal tests, did you purge before collecting them? You must take a high dose of laxative such as sodium picosulphate drops. It may sound digusting(and it is) but you must take a sample after purging, even if it's liquid. It's the only way to do it correctly, otherwise only a FRACTION will show in the lab.
You could try to convince you doctor to do one more sample?