It seems unlikely that someone would spike your food. They wouldn't gain anything by doing so, and they would risk a lot by doing so. It also seems like they can torment you just fine without it.
My advice, is that you should talk to a therapist. Weight loss and loss of sex drive are signs of depression (understandable given your stressful workplace).
Talking to a therapist will give you someone who will listen to you and give you a professional, non-biased opinion. Going to the doctor too is probably not a bad idea. Depression is a medical condition, they can check your hormone levels, but it is possible that something else is going on.
Please see someone to get help, feeling stressed is not fun.