Hi Sergio,
Careful of fish, most contain mercury. Some have lower levels, but if you are very toxic and sensitive, you may find you have problems with it. I choose to take a mercury free fish oil supplement instead (blue ice is apparently one of the best brands).
Yoghurt can be ok for some candida sufferers, because the lactose is changed into another form during the process and isn't quite the same as heese and milk as such. They are no nos. however, if you feel yoghurt is a problem, just leave it out.
You can eat as much butter as you want. In fact, the site I sent you advocates consuming a lot of it because of how healing it is. Again it is not quite like milk or cheese. and is actually very good against candida and hal Huggins recommends it for mercury too!!
You can have it in cooking, added to hot food, or some even eat it as is. Animal fats are proving very healthy for human beings and it's the hardened vegetable oils like canola etc that are quite toxic. You can find out quite a bit from the link I sent you. Don't be afraid of animal fats, be wary of the plant oils. The only vegetable oil that is fit for human consumption apparently is good old extra virgin olive oil!
I also consume the fat on meats with the meat. I do not cut them off. The extra fat in my diet has helped me, not hurt me.
The one that hurt me was vegetable oil (deep fried chips), I started getting heart symptoms believe it or not. I suffered light headedness, pressure and pain up the left arm etc etc. Very frightening. I stopped that very quickly.
Sometimes initally on this healing diet, you can indeed get symptoms and may make you feel worse for a time. It isn't easy but it is rewarding when you start getting a breakthrough.
Check this link out and look at the left for topics.
http://www.westonaprice.org/splash_2.htmHere is the link on fats
http://www.westonaprice.org/knowyourfats/index.html 
