Good day everyone! My cycle started after childbirth on August 6th, and…

Good day everyone! My cycle started after childbirth on August 6th, and there's a delay of 3 days in September. I think now that the test doesn't show definitively if it's due to breastfeeding or something else. Should I get my HCG tested? I'm thinking about it now...but yesterday I had back pain all day, probably period will come soon ?