If you decide to continue with them, don't go back to the same pharmacy to buy them. All of the major supermarkets can supply them very cheaply. (It doesn't need to be a branch with a pharmacy. They're on the open shelves alongside aspirins, cough mixtures, etc).
For example, they're currently £1.69 for 30 tablets in Tesco, but with a '3 for 2' offer on until the end of the month:
http://www.tesco.com/...Details/?id=263466800
If a qualified pharmacist has recommended them, then (assuming that you mentioned your blood pressure medication) you can have no worries about taking them. (Pharmacists know far more than GPs do about what's on their shelves!).
Vitamin B supplements don't directly give you more energy. For that you either need glucose or carbohydrates (which are broken down into glucose within your body). So that's a good excuse for 'pigging out' on some of your favourite foods!
However a lack of vitamin B can inhibit your body's ability to break down carbohydrates into glucose. So replacing the missing vitamins can help you to increase the amount of energy you obtain through consuming carbohydrates.
Chris