is a Beta Blocker
which is cardioselective a tachycardia you must know it was SVT or sinus tachycardia
as you point out you suffered cold
sometime a medicine for cold may contain sympathomimatic which may cause sinus tachy cardia or SVT ? but every thing is transient or subsides on stopping the drug. We also need to know any abnormality in ECG which may predispose to tachycardia. Beta blocker may be given to you for short time see your Physician. Beta blocker can cause many side effect including cramps but as you say there is loose motions also it may be due to Potassium loss also so seek medical help
you will improve give some time Physician is best person to stop metoprolol or not.