Inches aren't everything....
Doesn't that sound like innuendo?
Fact....if you eat right and train hard, you can't rely on numbers.
I lost body fat. Went from about 22% to 12%. I lost an inch on the arms and most anyplace else. I felt puny, but an honest look in the mirror showed veins popping out of my forearms, biceps, calves, and my six-pack started to show. My 14" arms depressed me, but a ripped 14" looks better than a fatty 16" anyday.
You might be overtraining....tearing down faster than you're building. Only you can be sure of that. If so, try working out less often each week (maybe 3 days instead of 5). I have to do that every now and then when I get burned out on 5 day/week training. I make gains, but spend longer workouts on training days. When that gets old, I go back to 5 day/week training and so forth.
You might not be eating enough. I'm on the MuscleNow program. If you aren't making gains, you up by 500 cal/day on intake and see what happens. You should have gains in either arm or chest measurements over time. If you are "bulking," you will put on some fat, but keep bulking until you add 2 inches to your waist. Then "cut" to get the fat off (drop 1,500 cal/day off the intake) until you get those 2 inches off and then up by 1,000 cal and see what happens. The program I use has pre-determined carb/protien loads for each meal.
Hope that helps some.