muscle weight?

damn man i used to weigh like 173 like 3 weeks ago the past 2 weeks ive been eatin alot and workin out with kellys program (lower body) and my nba power conditioning program (upper body) and now im 180 pounds!! in kellys vertical bible it says during the first week or so ur likely to gain like 5 pounds or so then as u go on ull gain less like 1 pound or 1/2 a pound a week…why is this? is it good that i gained that much, i really dont think its fat though i cant tell any difference in my gut or anything… any help on this topic?