It is very unlikely that your medication Montair FX (montelukast and fexofenadine) or your dust allergy are causing these specific blood results. Your feeling of weakness is likely related to your slightly low hemoglobin of 11.3, which indicates mild anemia. The elevated ESR of 50 suggests some mild, systemic inflammation rather than a simple allergic reaction. I reassure you that these findings are very common and manageable. Please share these results with your doctor, who can easily investigate further?perhaps checking your iron levels?to help get your energy back.