Hi Audrey, nice to 'meet' you.
It sounds like Markus is doing OK. Has he always been a quick eater or is this a new thing?
At around about 3 months, they become much more efficient eaters, your boobs have got used to their needs, and the milk becomes more rich, so I wouldn't be too worried, especially if he's putting on weight.
Does he go for long enough periods between feeds (i.e. roughly 3 hours), or is he 'snacking'? If he's snacking more often, he may not be totally hungry when you feed him, so try extending the times between feeds so he is more hungry, and will take more.
If that's not a problem, however, keep going - you're doing fine!
Caroline