Anal sex question....

I just started getting in to anal sex with my guy. He's slow, gentle and uses plugs on me. In the past most guys just try to go right in and it hurts! This guy uses plenty of lube and takes his time. My question is when he uses his fingers, why does it feel like I need to go poop? I don't really have to but it feels like it. Is he going too deep? Too many fingers? He's not a well endowed guy, so when we're actually having anal sex it doesn't hurt. His penis is soft for the most part. But when he's teasing me, I don't want it to hurt or feel uncomfortable like I might poop on his sheets. 🤦🏼‍♀️