Grieving is not wrong, it is good that you remember him and care about him. Stress is what's unhealthy. Try to remember your father in good ways, that make you smile. Be positive about it, remember all the good things he did and the good memories you have. Try not to dwell on losing him. Most importantly, talk about it. Keeping emotions inside will only stress you out and make things worse. Try talking to your mom or sibling(s) and reminisce about the good things, or talk to someone who has no connection with your dad so you can vent without worrying about their emotional connection. Most likely, this is a phase and you will get past it, but there's nothing wrong with remembering(: