Fml..poss 4th miscarriage

Waiting to get my HCG drawn..got a positive test on Tuesday at 3 weeks 3 days. Started having a slight back pain yesterday, no bleeding or cramping. When I took my first test the second line came up immediately but when I had one done in the hospital they said it took a while to show up. I’m afraid I’m having a chemical... this would be miscarriage #4 and I’m not sure how much more I can take.