Usually there are multiple causes for weakness. Dasatinib at your current dose is less likely to be the only cause of weakness. Anemia, Vitamin D deficiency, and other confounding factors need to be ruled out.

You need to regularly monitor your cell counts and monitor organ function. Weakness needs be investigated for any concerning issue like low blood counts, pleural effusion. If no significant cause is found and you are able to carry on with your routine work you may have to co to is with same. If no concerning cause of weakness is not found out then you may ask for change of medication like nilotinib or Imatinib. If any cause if found out like low hemoglobin then blood transfusion can be given. Please meet your treating hemato-oncologist in person for evaluation.