You can absolutely do a boudoir photo shoot while you are on your period. Every woman experiences her period differently and only you know if you will feel comfortable and confident during your shoot.
Tampon strings are easily hidden in your underwear and will not show up in the photos. If you prefer other hygiene products that are more visible, it would be best to schedule your shoot when you know you will not be on your period.
Most women choose to schedule their boudoir session when they are not on their period because of potential bloating and discomfort.
It is ALWAYS better to play it safe and schedule your session when you will be feeling your best. Most photographers will not allow last minute reschedules without a fee.