Does using 0.25mg of xanax (alprazolam) two times per week cause prolactin levels to rise? is it possible such a small dose could do that?

Very rarely, yes: The most common medicines to cause prolactin to rise, are antipsychotics through effects on dopamine. If you're also taking one of those, it would be the more likely cause. Usually benzodiazepines depress prolactin through their effects on gaba, but xanax (alprazolam) is different. By unclear mechanism, it can [very rarely] raise prolactin levels. Dose and frequency for this to happen is unknown.

Rare: Xanax, (alprazolam) very rarely can cause prolactin elevation and if you are prone to it, the frequency or dose may not matter. Most common psychiatric medications to cause this are antipsychotics by blocking Dopamine which helps control prolactin level. See your doctor and rule out other causes as well.