Extreme and prolonged stress can affect many of our bodies systems and how they function.
If you have lost only a pound or two due to your current level of stress, I wouldn't be terribly concerned, but if you are talking a substantial amount of weight loss, you definitely need to see your doctor. This can indicate a serious medical condition.
I've lost about 4 pounds last time I checked
I still wouldn't be too concerned, but while you say you haven't changed your diet, are you still EATING your diet?
Stress can kill an appetite easily and sometimes we have to make ourselves eat. If you don't have much of an appetite, this is a good time then to eat food that is not always our first choice when we're hungry. Instead of pizza, eat lots of fresh, local produce and fruits and veggies. Don't try to sit down to a big meal, just keep good healthy stuff handy to graze on. Smoothies are great for those times we're too stressed to even chew!
Jokes aside, just keep an eye on your weight. If you lose 10 pounds, see your doctor.
Do try to drink enough water. It takes very little for our bodies to become dehydrated and that DOES affect our stress levels.