Can vaginal atrophy cause a big increase in discharge, no odour and slightly discoloured? i was diagnosed with va and have a constant heavy discharge

It can but: Atrophic vaginitis can cause vaginal discharge but other causes are more likely. I would schedule a visit for testing for yeast and bacterial vaginosis. If those are present they can be treated. Vaginal estrogen is very effective at preventing atrophic vaginitis.

Yes: Many women do have a discharge associated with thinning and atrophy. As long as it is not colored, no odor, and no itching or irritation, it is probably normal.