I got offered a job nearly 3 months ago and still waiting for a start date?

I got offered the job nearly 3 months ago (in 2 days) and apart from the first load of paper work with my contract, occupational health and crb forms i have not heard from them since. I got my tests and clearances organised within a month and a half. I've kept my recruitment manager updated along the process and was told to wait to hear from them for a start date. Nearly a month later i enquired about a start date since i hadn't heard from them, turns out they hadn't heard from one of my references and if i could chase it. I did (my university tutor) and he said he had sent it to them at the beginning. He kindly said he would re-do it if he got the forms again. I told them that (by email, their chosen form of contact) 2 and a half weeks ago and that was the last i've heard. I'm still waiting and not sure what to do now. Continue waiting or try to contact them again. I'm desperate to work and really need the money, just came out of university, but i'm worried about pestering them in-case they can change their mind! They're a huge health care service/business so don't know why i'm being messed around.