The first thing that stands out, even from the first paragraph, is that you switch constantly from past to present tense. Doing so makes it hard to read. If you need to switch between the 2, make a definite break - a paragraph break or, even better, another chapter.
It’s starting to give me a headache, but it doesn’t bother me too much
You immediately contradict yourself here. Having read through, you mention his head beginning to pound further on, which makes the second bit redundant.
I feel like there's something missing. Maybe it's the lack of dialogue, or the introverted nature of the MC, but we don't really get much of a feel for what's going on around him. We know, for example, that he's surrounded by the usual patrons . . . But you don't really do anything with that fact. Maybe he could pick up snippets of their conversation?
Other than those pointers, you do a good job of setting the tone of the piece, and it's generally well-written. The MC feels real - I think we can all identify the kind of character he is, as does the bartender, and the pub they're both in.
I know how hard it it is to get the creative juices flowing again after a bout of writer's block, so well done for gettin this far.