Nah, Pharmacy peeps can't fill in sickness certs.
You generally CAN get seen the same by GP offices.....but it's a struggle and you need to get past the evil medical receptionists who's job is to stop you talking to doctors. Sick notes are pretty simple, takes 30 seconds to scribble out and they can do it any time of day and leave it for you to collect generally. (EDIT - this applies if they already know whats wrong with you, if you've never seen the GP about this issue before they'll still need to examine you, not all though, some will just issue it if you ask, party out of protest at the whole certifications system wasting everyone's time)
(For mine you basically need to phone them at 8am and say its urgent, they try and tie you up and ask if it's an 'emergency' so they can pompously tell you to call 999, you need to stick to your guns that it's urgent)
Is your college really going to give you much crap if you hand in the note a day or two late? see if yr visibly covered in swollen hives I don't see them arguing with you. (btw, if you've broke out in something that widespread unexpectedly and it's not going away, that IS the sort of thing you should get urgently seen for the same day, esp if it's bad enough it's stopping you work normally)