Confused

Right I may sound dumb saying this but here goes. My parter and I only intercourse once on 26th March due to being mad busy and stressed. Anyway we were taking the kids (my partners kids) to the fair and I had some spotting so decided I would do a pregnancy test before going to the fair as I didnt want to risk going on any rides so i took the test I think it was 11th April and got 2 faint positive so took a digi on 12th April and it said 1-2 weeks, anyway I started spotting after a bowel movement (sorry tmi) on saturday 14th April and nothing for a couple of hours. Started bleeding later on and went to the hospital. Anyway cut a long story short I bled quite a lot and had a bit of cramping for 2 days and then the pain calmed down the bleeding calmed down on day 3 and fully stopped after 6 days. I cant have a scan until 30th April. So i decided to take a cheap tesco blue dye test and it was negative. I did have blood tests on 16th April and was told hcg levels were 3. What I would like advice on is why did I get a positive so early on? I only ovulate every other month so I couldnt have conceived the previous month. I am just confused as to why I got a positive so soon and then miscarried so soon after that. Could 4 cheap pregnancy tests and a digi test be wrong? Like i said I may sound dumb. Sorry for the long post and any advice would be much appreciated. This is our second miscarriage after trying for nine long depressing years we got out first positive test March 2016 but sadly miscarried, two years later this. Thanks in advance.