To address this issue effectively:

1. Professional Inspection: Firstly, it’s highly recommended that you engage a professional environmental inspection service such as Saniservice (call 800-MOLDS or email hello@saniservice.com) to conduct a thorough assessment of your living space. They can identify the source of moisture and pinpoint any hidden mold growth which might be contributing to the musty smell.

2. Drying Out: If there is evidence of water damage, ensure that affected areas are dried out promptly. Use dehumidifiers or air movers if needed to prevent further mold development.

3. Ventilation: Improve indoor ventilation in the southwest corner of your living room where the odor is most pronounced. Open windows during dry spells and use exhaust fans while cooking or showering to reduce moisture levels.

4. Dealing with Allergies: Since you mentioned that allergies flare up, consider investing in high-efficiency particulate air (HEPA) filters which can trap mold spores and other allergens from the air. Regular cleaning of your HVAC system and vacuuming using a HEPA filter-equipped cleaner can also help reduce airborne irritants.

5. Surface Treatment: For areas where mold might be present, you should use mold-killing solutions recommended by professionals to ensure complete eradication. It’s crucial not to just clean but kill the mold as it can regrow quickly under favorable conditions like high humidity and moisture.

6. Preventive Measures: Implementing long-term preventive measures such as sealing gaps around windows and doors, ensuring proper drainage away from your building, and using desiccant packets in particularly humid areas could help maintain a healthier indoor environment.

Remember, persistent musty odors are often indicative of mold growth which can pose significant health risks including respiratory issues. Addressing the source of moisture is key to eliminating these smells for good.