Since your period has started then there is nothing now to stop it although taking mefenamic acid may lighten the flow.
As far as hiking is concerned, then having your period will not be an additional concern as long as you don't have heavy flow and cramps. You may want to take along the portable 'heat pads' that are self adhesive to clothing as these are very good when keeping mobile. Do ensure that you maintain your energy intake with carbohydrate and adequate protein and iron levels too. Take some ibuprofen with you for period pain if you don't use mefenamic acid.
Aside from that you will have the inconvenience of tampons, or you can use softcups 'insteads' which are available at drug stores and can be left in for 12 hours.
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