Excercise in first trimester - have you been able

Hi I am 13 weeks and had hoped that while I was not showing I was going to be able to continue to excercise but I have found I haven't been able to anything except go to work and then lie on either the couch or bed. This is because of a combination of tiredness and nausea . Have not been able to stomach healthy foods anymore and so have not had the best diet and with being sedentary have piled on the weight. Just feeling pretty miserable and wanted to know if other people were going through the same thing ? Both my sisters and friends in first trimester did not seem to have the weight gain like me and I feel like i prob should just be bucking up and going for a walk but just feel so rotten!