Anyone that can help me is much appreciated!

Tested positive on week of missed period when I went in to my OB urine test there wasn’t picking up so I had a blood test (feb 5) after the result showed 15hcg they had me test couple days later and came back at 85hcg. Since the beginning the nurse was treating me as a threatening miscarriage bc of the number so I was annoyed from the get go. Fast fwd a wk later I started with lower back pain and lingering mild cramps so I got worried. Cramps reminded me of period cramps so every time I’d go pee I would check and on the 15th I peed blood and that’s when I headed to the Er and blood work came back at 40hcg and in the ultrasound they did there there was no sac at all. How could my body betray me like this and make me feel pregnant and give me positive result all for nothing . Anybody gone through something similar??