Midwife is preparing us for twins!!

So we had our positive 4wks ago but I already had sickness sore boobs and other symptoms way before we got it!!     had my implant out the same day as my period the 12th of November and had what I thought was my next period 3wks later 5th of December...anyway I've just had my first midwife appointment as in Somerset you are not seen till 8 -10 wks but According to my date I was 5 wks (going from the 5th Dec) but my sickness got worse so much so the doctors put me on medication and I sleep for 18hrs a day (totally wiped out) anyway tummy is huge and I look like I'm 20wks pregnant....still waiting on my dating scan to come through.....but had a shock when the midwife said she is putting me down as 11nearly12wks pregnant and the kind of sickness and tiredness and weight gain is normally only seen in amultiple pregnancy......NOW IS PANICKING! Anybody else had this??? We're your midwives wrong?? Xxx