Are these muscles or just fat?

Rebekah
Hi, ladies! 
I rarely ever ask questions but I've been going through some issues with gaining weight due to PCOS. Recently I've noticed that my arms are a lot bigger than before. Like they have never been small to begin with but now they look "lumpy" however they also look muscular. I have been doing yoga 2x week since February so I'm sure I've toned up from that but my arms are still bigger than they've ever been fat-wise. 
I don't know if I explain it well but there is definition sometimes:
My fore arm flexed 
Full arm working 
Full arm relaxed 
Could my muscle be building up under the fat and I'm just not losing the fat? I don't concentrate on losing weight because the PCOS makes it difficult.  This may just be a dumb question and me just concentrating too much on it all 😂