Hair smells like egg?

So I've been using the same shampoo and conditioner for 3 weeks and it's been fine until the last few times I've washed my hair, it's got a rotten egg smell to it and the products are not smelling, so I changed my shampoo and conditioner incase and the smell is still there I can't get rid of it? I thought someone pranked me and put hair removal cream in there but they haven't (I don't think) how can I get rid of it and do you know what might be causing it? Any advice will be greatly appreciated