Right now this is all that Zorro has said to me, I drank the potion when I was told to, and that's where I got left off, nothing else has happened after that and it's been days searching all over the place
Sorry, can't think of anything else. You might want to raise a bug ticket, since that quest should have ended as soon as you met Bloodthirster at the gym after taking the potion: https://blackcatstudiosdev.atlassian.net/servicedesk/customer/portal/1