Is what is happening to me—the fulfillment of dreams, knowing the gender of a pregnant woman's fetus, and hearing voices in my sleep telling me about future events—a good thing or an evil, especially since knowledge of the unseen belongs to Allah alone?

If the questioner holds sound beliefs, then her awareness of certain unseen matters, or their occurrence as she described, is a sign of good and does not contradict Allah's absolute knowledge of the unseen. Allah may reveal some of the unseen to certain righteous individuals, as happened to the divinely inspired (muḥaddathūn), among whom was Umar ibn al-Khaṭṭāb, may Allah be pleased with him. This includes true dreams, which are one of forty-six parts of prophethood, and are considered a karāmah (divine grace) for the righteous servant who strives for truthfulness and piety. Some of these matters may also come through sagacity (firāsah) and contemplation, as occurred to many of the righteous predecessors (salaf al-ṣāliḥ).