Pregnant. Why Bleeding In Dark? Why Did Next Ultrasound Show Empty Sac?

Hi, I m 31 had 2 kids the youngest is 4 now. My last period was on 28 June and yesterday had an U/s which showed I m 4 weeks and 5 days pregnant. On 11 of august had intercourse with my husband and it was deep penetration, next day in the evening I had bleeding which filled a pad it was dark red and like a rubber but stopped and continued to be very light till today if I use the toilet and push the blood appears as a line and discontinue , it s dark red in colour and rubbery, next day I went for an u/s which showed I m 4 weeks 5 days and my sac was still empty. Till date 14/8 I m still having light bleeding appears only of I m in the toilet and it s dark red and rubber type. Is everything going to be alright , my dr. Asked me to come next week for another u/s but I m so worried and time is killing. I want my baby to be sAfe