I am sorry to hear that you are constantly feeling stressed. It may benefit you to talk to a counselor or therapist
to help you sort out some of these feelings.
In part, learning to cope with stress does involve learning to develop good boundaries. Many people who are stressed and overwhelmed get that way because they do not know how to say no to new projects at work, etc. A counselor can help you identify any of those tendencies you may have and develop strategies to overcome them.
There are several lifestyle things you can do as well that will help with stress. These include making time to have regular, healthy meals (rather than just eating on the go), getting plenty of sleep each night, and engaging in regular aerobic exercise on most days of the week.
You should also talk to your primary care doctor or psychiatrist
if you have any symptoms of depression or anxiety. These two conditions often coexist with stress, and they can make it impossible to cope properly. Fortunately, both of these conditions can be treated with medications, so it is worth ruling them out so that you can move on.