Should I shadow a pharamcist for a few hours a week and then later ask them for letter of rec or tell them beforehand that I want to shadow them and wish to get a letter of rec? Also is it okay to just ask previous professors for letters from like bio/chem classes? Do they usually have like a letter ready made or do they need to know me really well, because I'm not sure if they will remember me... I do go to a pretty big school. I'm just not comfortable asking for letter of recommendations, I feel like I'm bothering them.