am I being a pest?

I can't help but to feel depressed coming into work being asked to do something I have not been properly trained on.  Granted we have gone through some of the different what-if scenerios in training but I need more reassurance when working on the real projects especially because nothing's ever straightforward and a tiny mistake could impact so many other things and I'd rather be dead sure before I do it.  Yet I have found no help from my coworkers - they want me to help with the workload but at the same time they can't spare the time to show me how it's done.  I hate to be a pest and I hate being bounced around the office - but I have to constantly ask others and consistently get turned away until I mention it to my manager, who in turn would send out a request to have it done.  By then my coworkers would have to give me a hand willingly or not - and usually not.  It's been so stressful that I feel like it's turning me into a different person...