Yes, Most ulcers are bacterial. The infection isn't localized though. So if you have an ulcer, the rest of the stomach lining will be infected, too. This will decrease the stomach's resistance against it's own acid while hindering the mechanisms that tell the stomach to stop producing acid, along with gases that form when the stomach didn't digest something properly and the bacteria that infected it did that instead. All of this will increase the pressure and the vulnerability of the stomach.

By inhibiting the stomach acid production, the stomach's skin gets a chance to heal itself. That's why proton pump inhibitors are vital when dealing with an ulcer. Depending on the specific case, antibiotics are used in combination with proton pump inhibitors. The bacteria that causes ulcers are usually fairly easily killed with antibiotics. The fact that your symptoms worsened might tell the doctor that the dose of specific proton pump inhibitor are inadequate.