I have experience in this field actually. I was co-founder of a high quality feminine napkin company, Empower Pads, where we used a green homeopathic strip which helped women with things like ICT, urinary tract infections, cramps, etc. (http://icnetwork.empowerpads.com/)

We never did sell a monthly subscription though, we went to a lot of trade shows and tried some JVs with custom online sales pages like the one above.

In the end we found that the product was too difficult for us to move because people don't like to talk about pads and tampons. Its not really a big 'referral' product. It helped thousands of women, we got hundreds of amazing video and written testimonials & reviews, but it didn't take off for us.

You could look into the product Poo-Pourri (http://www.poopourri.com/) and see how they created a viral video campaign for a similarly difficult product to market. Their video and sales page spread by using comedy to sell something that people don't feel comfortable talking about.

Another good monthly sales subscription to look at in the personal & grooming space is Dollar Shave Club (https://ca.dollarshaveclub.com/). Although it's not extremely relevant to tampons & pads because men don't have a problem talking about razors.

You could also try sponsoring podcasts with similar interests.

Hope that helps.