DO NOT USE IT DURING YOUR PERIODS! You're supposed to be low in progesterone at that time. That will mess up your natural cycle.
The reason it says that on the bottle is to protect themself from any liability. In reality, if you're low in progesterone, then your body needs it and it will help your body to have better and stronger ovulating cycles, which will help you to become pregnant.
My Dr. put me on it several years ago. I use a prescription strength all natural compound progesterone cream. I use 50 mg twice daily for 10 days, starting 3 days after I ovulate. Now, it's tricky because it's necessary to chart your cycles and know when you're ovulating for the progesterone to work properly in your body.
Just a little FYI...the first half of your cycle, estrogen is elevated and progesterone is low. Once you ovulate, your ovaries send a signal to your pituatary gland to stop ovulating and thus will send out the message for your body to produce elevated progesterone. Your level will increase over the last part of your monthly cycle and then drop right before you menstrate.
So, if you're low in progesterone you likely will have some nasty PMS symptoms and you might suffer from infertility and/or miscarriage problems. I started on the progesterone cream because of really bad PMS that started about 10 days before my period. I felt CRAZY! The progesterone greatly helped me out. Also, I always ovulated late in my cycles...around day 21 or later. After being on the progesterone cream for about 6 months my cycles changed and I started to ovulate on day 16, which was a miracle for me. I hadn't ovulated that early in years! Because of all this, I eventually got pregnant and now have a beautiful 5 month old!
I recommend you talk to your OB about taking this cream. The OTC creams are only 20mg, I believe and tell you to start using it around day 17 in your cycle;however, if you really are deficient in progesterone, it's likely your having ovulation issues. Your dr. can do a blood test 7 days after you ovulate to tell if you're low.
I hope this helps and isn't too confusing. I've dealt with this issue for a long time and know how frustrating it can be.