I am assuming this 13 month-old is your first child?
Please just stick it out with the NFP. Fertility returning after childbirth can be long, slow process which is frustrating to those who have reason to postpone another pregnancy, and breastfeeding can make it even more confusing and drawn out.
After the birth of my first son 3 1/2 years ago my husband and I finally learned NFP. We started charting after our son was 6 months old and I had a return of my periods at 7 1/2 months postpartum. However, I never ovulated until 11 months postpartum. Breastfeeding was suppressing ovulation even though I was having periods every 30-45 days. It was an extremely frustrating time for DH and I. However, it was only a few more months before I started ovulating regularly and we could see a distinct pattern and abstain less. Then we decided to try for baby #2 anyway.
Those 5 or so months were extremely frustrating for both of us, but I am so glad we stuck with it. It meant we didn’t disobey God by using contraceptives, and it gave me tons of information about how my body works after pregnancy that I could apply to baby #2.
Just stick with it. I know it’s hard now and it seems like there is no end, but it always seems like that when we are in the midst of a problem, doesn’t it? It’s not hopeless. Pray a lot about it. Know you are doing the right thing and that God will take care of you. It will only get better each month that goes by and soon you’ll be having regular cycles that are easily charted and you will be able to abstain less.
God bless!