There is a LOT of complaining in Bamidbar. Why? Like Rashi says - a תואנה. They looked for pretexts to complain. That is a rule of complainers. Most complaints are saying the same thing - I am not happy. It is not about the particular thing they are complaining about. Happy, healthy people look for every reason to feel and express ... gratitude.
If you want to be happy - invest in relationships, in your deeper spiritual life, eat, exercise and sleep well, focus on increasing self awareness and always be kind and loving. And like I just wrote - constantly always look for reasons to feel gratitude and Baruch Hashem there are endless things for which to be thankful.
