I definitely agree that you need to seek a vet who can help you properly diagnose. I don’t have any experience with treating a bp for an RI but I would not treat them with anything right now. As stated, wrong antibiotics will only worsen the situation, and if it’s actually viral, then it’s not going to help at all. But there are some things you can do to help your snake out temporarily until you seek medical assistance.
You could place a branch inside their enclosure that’s elevated(diagonal) so that they can rest their head both up and down at a 45 degree angle. You’ve increased their temperature which is good. And really try to keep the humidity at 60-65%. 70% is okay but I would not push it any further. Lastly, take a look through the enclosure and make sure there isn’t any type of mold, bacteria growth, feeces, or urates. Also clean out the water bowl, and make sure to replace water daily.
Do you know what stage your snake is at? It would also be good to know to determine what other actions you need to take and if there is anything else you need to look for.