Exercise after treatment

Well here I am one year post diagnoses - having had a WLE, lymph node clearance, 3xFEC 3xTAX chemo, 29 rad sessions. Have felt battered and bruised but am here – happy (well most of the time ), hair is growing - although very curly but its hair, and now is the time to give a little bit of love back to me – the weight is going albeit slowing (I am still blaming the steriods even though the last course i took was November!)
So now is the time to love the new me – wear my scars with pride and to look in the mirror and say “your a tough old bird and I love ya!”
I have decided that my post cancer body will be in better shape than my pre-cancer body and so with that in mind the diet has started and I have started to build my fitness up with some walking/running and will be fundraising through a 13 mile walk later this year…
So my big question is – can I use some light weights without irritating my affected arm – have brought one of those shake a weight dumbell’s and now too scared to use it just in case I do more harm than good…
Any help with this quandry would be great – thank you
Wishing you all best wishes