This problem with you of loosing weight and that too which is very much significant can be because of many reasons.
The description which you have given it is not clear what can be the reason. The common things which can be there are like depression
causing loss of apeptite and causing weight loss
, some sort of chronic infection causing this weight loss, deteoration of general condition due to some immunolocal condition.
So there are many more condition which can lead to this type of problem. I would suggest you to consult some doctor regarding this and only after proper history taking and examinationa and if required some investigation, it can be made clear what is causing this problem in you.
Thanks and take care