If it's only been four months, then you don't have to worry. To make deeper than surface level connections, find a group activity and show up repeatedly (this can be work or school as well). But perhaps the Japanese aren't too interested in making friends with foreigners? The part about moving I mentioned is also about moving to a place where people are more sociable, I don't know if Tokyo is it.

Permanent mental damage is rather from years spent in loneliness, or lovelessness, or poverty, or any other kind of unsustainable personal situation.