Hi RCC
I'm so sorry about of the loss of your mother.
I know when my father died, he'd been suffering from liver cancer and we new his time was near yet it came as a terrible shock and took a long while to get over.
Medication does help as do talking therapies but you need to see your doctor and discuss it with him/her and take from there.
Jaq's post above gives you some very good pointers.
Edit:
I've just read Suzi's post and bereavement counselling such as Cruse are a considerable help.