TTC while Breastfeeding ?

Stories welcome, currently TTC #4, app said I was due for a period 2/3, I have missed it and have tested negative for pregnancy. It’s been 21 days since unprotected sex other than today so I’m safe to assume no pregnancy is possible. I’m not sure when or if I have ovulated at all. My baby doesn’t currently take breast milk more than 3 times throughout the day and once over night. Majority of her diet is baby food so I’m not really sure what is going on. Should I start trying to track my LH and bbt until period shows up? Or wait another 2 weeks to test again? Should I start taking certain vitamins or consult my OB? This is all really new to me, and my pregnancy before was by surprise. Plan on getting married 5/5 so would like to try to conceive before dress alterations. Thank you!