Pregnant and Breastfeeding?

So I’ve got a little guy who is 4 months. My husband and I have fertility troubles and we chose not to use birth control in between children (I know there is a risk). I should normally be able to get pregnant but have a blocked tube so it makes it more challenging. The last few days I’ve been feeling a little funny and crampy/pokes. I don’t know if it’s my period trying to come for the first time, gas, or a possible pregnancy. I’m wondering if you got pregnant while breastfeeding and before your period came back, how did you know to test? I tested earlier this past week and it was negative. Maybe just my period 🤷🏼‍♀️