Strange. That’s not really how antibiotics work. They work on bacterial infections and not a virus, plus you need to take the correct antibiotic depending on the bacterial infection. You can’t just take random antibiotics hoping it will get rid of some unknown ailments.
Most of the Irish bars in Bangkok are your standard fare. BS seems to have better quality products and more stuff cooked from scratch rather than just microwaved. They do a very good breakfast and the fresh sausage rolls are lovely.
Go onto booking.com or Agoda. Look at the map and book anything between Asok and Nana BTS stations. That puts you in walking distance of Cowboy, Nana, and Soi 6.
The guard shouldn’t/can’t stop you. You could be a guest, or you could simply be walking through to Soi 2. It’s none of his business. If he tries, be polite, but just ignore him and carry on walking.