Losing weight after leveling off!

sgfoster110

I lost 40 lbs 3 years ago and recently tried to lose another 10lbs. I have been struggling. I think the reason is I have been maintaining and building my muscle strength. I am larger now througout my shoulders and arms. I am correct in thinking the reason is muscle not fat? I don't have much fat anywhere. Just a little at my tummy. Thanks for any answers.