What is the ruling on money I acquired from analyses I secretly conducted in a medical laboratory, and how can its value be estimated to return it to the laboratory?

What you did by performing analyses for your colleague without the permission of a mahram is something you must rectify by returning the analysis fee. If you do not know the amount you need to return, and you cannot inform the doctor to find out what you owe, you can err on the side of caution with the right until you are certain that you have fulfilled your obligation and cleared your conscience. Ibn al-Arabi said in his Tafsir: "One should err on the side of caution in this matter until no doubt remains in his mind, and his conscience is cleared of the forbidden." So, rectify what you wrongfully transgressed by returning the analysis fees, unless someone authorized to grant absolution absolves you. And do not repeat such an act.