Period? Pregnant?

So my baby is almost 5 months old, and I bled for a few weeks after having her, then it stopped and a month later I had some bleeding for a few days again, then it stopped. I haven’t bled since then and I’ve had some occasional nausea, headaches, and just feel kind of off. The first symptom I had when I was pregnant was shortness of breath. My husband and I use protection but I just wonder if I’m pregnant again. I breastfeed but also supplement with formula sometimes.