How would you know if you've had any problems? You have brain damage
You should be fine. There's a lot of conflicting info and opinion on it. The mercury amounts are very small. Your kidneys can handle mercury pretty well if you don't suddenly up the amount all at once. Some gets excreted by the gut. I wouldn't go hog wild and eat 3 or 4 cans a day every day. Some may get stored in the brain, and other tissues. It's general considered safe in moderate amounts. Plus the only way mercury can cross the blood-brain barrier is that is binds with methionine and looks like it to the brain. But that will be inhibited by all sorts of other large aminos in a high-protein diet.
Stick to the "light" tuna which has less mercury and avoid the albarcore or "white" tuna.
There is a difference between acute mercury poisoning and chronic mercury exposure in small amounts. Your body can deal with the latter much better. And in fact there is data to suggest that once storage levels of mercury reach a certain point they level off and it doesn't get any higher, all of which you don't need to worry much about if you just use moderation, like with everything.