Constant constipation - nothing working

I've been constipated since I started on effexor. I read on here that probiotics help, so have been taking them for around a month and it's made no different. I am drinking lots of water and doing light exercise. My doctor has prescribed me a stool softener, but it doesn't do anything.

I've also tried prune juice which has not helped. I have bought some laxatives which sometimes work, but don't really want to take them regularly....

I bought some Metamucil but saw on the bottle that you shouldn't take it for medicine induced constipation - does anyone know if this applies to venlafaxine or if it's just opioids?

Any other suggestions would be much appreciated! I would prefer not to stop taking it for now