No doubt it is possible stress can cause all of the above. If I we're you, I would really try and keep my distance between you and his sister. She seems to be the real culprit right now. Being pregnant is hard enough without having to go through that with her. I think if you stay away as much as possible, you will find you feel a bit better.
At 4 months, you are going to start having some abdominal discomfort as that little one grows. Just wait till it's feet are up into you lungs at about 8 months along. Now that is really fun. NOT! Sometimes even hard to breath and ya have to stand up and hope he/she repositions itself.
By no means take any medication without first consulting your OB.

I wish you the best for the three of you.

Carrie

I'm sorry to hear that you're not feeling well. Maybe try to put your feet up for 20 minutes. This helps stimulate the relaxation response and can help in times of stress be careful though, b/c you might be tempted to invert if you feel tingling...but keep with it.