does dextrose contain any fructose?

It does not contain fructose.

Both are forms of sugar, as are glucose, sucrose [table sugar], maltose, lactose and indeed anything ending in 'ose' is a sugar. Notable exception - cellulose - this is not a sugar, but a dietary fibre. You would be best to see a dietician/nutritionist, if you live in GB your doctor will refer you, and you should be able to see one on the NHS. 

It is best to avoid high levels of sugars, especially refined, added 'free' sugars. If you are wanting to sweeten drinks such as tea and coffee, try stevia, short term [this is a non-sugar sweetener, but is a natural plant product, and therefore does not have the health issues associated with artificial sweeteners such as aspartame and saccharine. Slowly phase it out until you can drink unsweetened tea/coffee.