Needle questions

Okay I've been tattooing for a few months while doing a tattoo after a while (and even faster in fattier areas) my needles start going in less smooth and feel like there catching the skin and they kind of pull it sometimes it seems like the needle goes in and then when I'm moving my hand it catches a bit and skips. I was wondering if this was due to the needle dulling because upon switching to a new needle it will flow much better. But especial in the fatty areas it seems to dull real fast. I was wondering is this normal or is it my machine isn't calibrated right or is it just me using it wrong? Thanks