Light and watering are the most likely issues.
Light: Full sun. Move your sprouted guava to a very sunny place as soon as possible. During summer, move outside to a sunny patio. In the winter, move inside to the brightest location possible.
Water: Provide regular water during the growing season, and reduce watering during the winter.
Soil: A rich typical potting mix will do fine. Good drainage is important to protect the roots.
Fertilizer: Feed with a weak liquid fertilizer throughout the growing season.