During the fermentation my mash stopped bubbling after 5 days! Can yeast be added? I think I didn't put enough the first time!!
The only way to tell if fermentation is done is by taking hydrometer readings. If the gravity numbers don't change over 2-3 days, it's done. Do you know what the target final gravity is? If fermentation is done and you're close on the final gravity, then no worries.
OK, I assume you mean "wort" not mash After 5 days it might very well be done fermenting. What temperature did you ferment at?