Further on?

My AF is due 12 May and on Sun 8 May I felt light headed & sick so took a test. Within 30 second two lines appeared (see pic). 20 mins later I took a ClearBlue digital and that was positive. According to Glow I am 3w 5d. I have been taking more tests and all are positive. I even have take two tests that claim can only be taken from the day of your missed period, and they have came up positive. All this suggests that my HCG levels are high. Could this mean I'm further on or possibly expecting twins? Have any of you experienced similar? Midwife appt isn't until 31 May but already have so many questions!