Light periods

The last few months I've had lighter periods but this month is super light. More than spotting but I could easily just use a couple of panty liners rather than a tampon each day. I'm underweight but I have been my entire life as I have marfoid hypermobility so my bones are smaller and I burn calories quicker. Never had problem periods before.  I am trying to gain weight though. Anybody else experience this?! Could I be lacking estrogen or something? Been ttc for 8 months 😞