Hi, welcome to the forum, myalgia is not common with amoxicillin. It is reported in 5-7% patients who are on actonel which contains risedronate. Body ache is usually seen in some generalized conditions like anemia, abnormal sleeping posture, viral infection (with or without fever), Depression, electrolyte abnormality etc. Even hypothyroidism should be ruled out as fatigue and body ache is its classical symptoms.
Hence, baseline blood tests should be limited to a complete blood count, erythrocyte sedimentation rate, standard blood chemistries, and thyroid function tests. Meantime, having nutritious food, OTC pain killers, skeletal muscle relaxants against prescription, hot water bath and body massage will help. I suggest you to consult physician for detailed evaluation and treatment of the cause. Take care and regards.