I have 3 children & have never had a miscarriage but have been under a lot of stress lately. Should I wait awhile to tell my family that I'm pregnant?

Depends on situation. Family can be a great source of strength & support or a battlefield of emotional turmoil. If you find strength in yours, let them share the good & possibly sad moments of your life.You don't need to shield supportive family from your true feelings. If they are the source of your stress, build your support system elsewhere & involve them when you feel ready.
Perhaps. I would suggest you have a pregnancy test. An ultrasound is even better if the test is positive. An ultrasound finding a live 8 week embryo has less than 3% chance of loss. So that is a good bench mark to reach and is reassuring for the future of your pregnancy. Best wishes to you.