Wierd Weightloss...?!?!!!?

Hi, I am a 49 year old male, who is about 5'7" in height and normally 170 lbs. in wieght. recently (over the last month or so) I have lost almost 10 lbs. But the weird thing is my diet is almost exactly the same, (as last month) and I am excising even less because I hurt my knee. The only thing I cut out of my diet for one month was alcohol (specifically beer).. Is that something to look into, or is it really the alcohol. Especially answer this if you have a education in medical needs or weight loss, thank you.