Liposuction, NN :-)
Seriously, if you've shifted 8lb in a month then it's unlikely that you've only lost fat. You've probably shed a bit of muscle protein and a chunk out of your glycogen stores too - which might explain the higher body fat percentage.
Alternatively, the accessible forms of body fat measurement (Tanita scales and Omron hand-held monitors) are dismally unreliable. As far as those machines are concerned, the difference between 15% and 18% is probably within their margin of error! And both figures are well within the normal range for a man.
Do you FEEL fatter than you were before? If not, throw the scales away. If you fail the "wobble test", eat plenty, aim for a carb-rich athlete's diet, and increase your training a little, making sure you include some resistance work. But I'm sure you're just fine.
Cheers, V-rap.