Cleanse and protect is the best idea magickally speaking but how we you sure he's cursed? People go through highs and lows in life, and not everyone is an optimist. If you are worried, ask him to see a doctor, his misery could be a health issue [lack of vitamin D] or maybe a mental issue [depression] or he could just be an introvert.
You could also go for spells to help turn his luck around or find a job, but if he's not willing to work to change his life, the spells will be pretty useless. Cleansings and protections are a good idea even if there isn't a curse, negative energy can build up over time, so it's a good idea to do this regularly. If this is a curse, or just a mild bump in the road, remind yourself [your son] you've washed away all the negative and should charge with positive. If it's depression or something medical, speak with a psychiatrist or doctor and get help. Whatever happens 'just keep swimming' and look on the bright side best he can.