There are actually quite a few types of antibiotics. Most people don't hear about most of them because they're reserved for specific infections (oral vancomycin for c difficile, isoniazid/rifampin for tuberculosis, linezolid for MRSA, and carbapenems as a last resort). Most common bacterial infections are treated with common antibiotics to limit bacterial resistance.

If a bacterial infection is resistant to treatment, additional antibiotics will be added in combination. Investigational antibiotics may also be used if the benefit outweighs the risk. Currently there are studies being performed to try and identify antibiotic (or other drug) combinations that more effectively kill bacteria. Some drugs work together synergistically (IE they're better together than expected) while others antagonistically (IE they work against each other) and it's not clear why.

Treatment options for multi-drug resistant bacteria - www.frontiersin.org/articles/10.3389/fmicb.2019.00080

Assessment of drug interactions - https://www.science.org/doi/10.1126/sciadv.1701881