I'm really confused and worried about how far along I am and my hcg levels pls give me advice!

So I went to the hospital today because I kept on spotting for a week but he said that was nothing to worry about it was because I apparently have A- blood and the baby has a+ blood so our blood was mixing and not working well together so my body was getting rid of it but he said that that is ok it doesn't hurt the baby at all but then he made me worry because he thinks I'm actually earlier in my pregnancy which makes sense I think my doc calculated my due date a little weird so I'm only 5 weeks but the doc said that my hcg levels are definately positive and getting higher but in week 4 I had a hcg level of 48 and this week (we thought I was in week six but now think it is week five actually) and I'm not sure of the number but he said if I am in week six it is on the lower end of the scale for that week which made me very nervous but if I am in week five I guess it is totally fine I'm just so nervous now has anyone experienced anything like this before? Pls help