I had an apendicectomy 10 days ago and i've lost some weight (i lift weights at gym) and i feel thin now. so my question,is it normal to lose weight?

Yes: Even after relatively minor abdominal surgery (I presume you had a laparoscopic appendectomy) your digestive tract/appetite/bowel function is disrupted. Many people just don't feel like eating for a few days. Eat as much as you are comfortable with and notice when your bowel function returns to normal. You may need a little extra of your usual healthy diet to slowly regain to your desired weight.