Since diphenhydramine hasn't helped, your symptoms are likely from a viral cold rather than allergies. The chest and neck pain is common and usually due to muscle strain from coughing. For relief from body aches and soreness, try generic acetaminophen or ibuprofen. For the cough, consider dextromethorphan to suppress a dry cough, or guaifenesin to help clear mucus if it is wet. Ensure you stay hydrated and rest. If you experience shortness of breath, a high fever, or if the chest pain becomes severe or constant, please seek medical evaluation to rule out any complications.