Confusing dates

Chelsea • KMML 4.14.14 💜 TML 12.13.16 💙
First of all, my periods have always been normal. Then all of a sudden in august of '15, they started skipping a month. I started taking clomid in december, and stopped taking it in April. I had a period after stopping it, right on time. My last period was March 1st, lasted a full 5 days. My husband and I baby danced on the 9th, 13th, 16th and 18th. Glow said I was ovulating the 14th thru the 20th. I got 3 faint positives on March 28th, followed by a positive blood test. My HCG levels on 3/30 was 24, 4/1 was 44, 4/7 was 517, 4/9 was 1022. I was given a due date of 12/7. I had an ultrasound on 4/20 (7+2) and only saw a gestational and yolk sac. I went back on 4/28 (8+3) and saw a heartbeat. The tech measured the fetus and said it measured 6+4 and suggested a new due date of 12/18. How is it possible I am only 7 weeks if I found out 5 weeks ago that I was pregnant? I know late ovulation and what not but how is it even possible to find out at 2 weeks pregnant?? And if I ovulated late, how could I find out just mere days after a "late ovulation"?? I'm so confused.