Stomach flu or period? Normally I start around the 5/6th ish of the month. But right now and for the last day I’ve been having symptoms?

Like right now my lest arm (sometimes both at the back and around my underarms back ache and my stomach hurts and like over got a headache weirdly at the top and back of my head and I feel a little sickly. Bare in mind I haven’t been out the house in 3 days.