If you have an abscess it's largely going to be that causing pain. I remember when my wisdom tooth became infected once the antibiotics kicked in it might a massive difference and the shattered tooth was bareable.

Well done for getting it done. Did you tell the dentist you hadn't taken these? Please bare in mind the infection is still there and whilst the dentist has tried to clean your mouth you still need to take the antiobiotics.

Whilst you fear it, delaying could lead to a more complex problem as Mouse says. You don't want that, the antibiotics you could be on then may come with more appararent side effects as opposed to your current one which is a low level one by comparison.

Get a strategy in place. Take it with someone there to help. Put it inside some food if you have too.

When I feared taking things it was about once it being in my body I couldn't do anything and my anxiety would rise. I would fear rises in anxiety or side effects that could make me feel worse as my anxiety levels would raise.

Don't stand there building up to it. Walk into the room and neck it. Walk out and distract yourself. You may see anxiety increases at this point but it will fade over time.