I barely cum when I orgasm while bottoming, is that normal?

Whenever my boyfriend and I have sex, I barely cum, even though I climax. If he fingers me, I cum a lot and when I'm just jacking off I cum a lot. But when we have sex, sometimes I don't even cum at all. Is this normal? I've been tested recently and I'm all clean, so I just wanted to know if any other of my fellow homos experience this.