I'm 14 weeks pregnant and have lost 7lbs had morning sickness ended 2 weeks ago. Also was wondering if constipation can cause you to lose your appetite?

Rarely. Only if really severe. Take stool softeners, fiber supplements, eat your fruits and veggies and drink lots of liquids. Usually your weight will have no problem rebounding.
Sometimes. Constipation if there is severe backup can effect appetite. It can also be related to your vomiting and loss of fluids. The mainstay to treating constipation is adequate fluids in the diet.