I'm lost.

I had a faint positive last Saturday on a FR and a negative on a cheepie but started bleeding alot that same night. It lasted two days and stopped. I called my Dr on MONDAY and he said to take another test to see if it was still positive before i could resume Letrozole. It was and I had to go in for blood work Tuesday. They called me on Wednesday and said my level was only 18. So I needed to come in the following week to test again and make sure the level went to zero. Well a few days ago I started getting ovulation type symptoms and I heard you can ovulate quickly sometimes after a cp or a miscarriage. I didn't want to miss my chance. This whole time though I've still been nauseas and having to pee pretty often and my boobs have still been sore. I took and opk last night to see and it was positive. So today I decided to take another opk and a pregnancy test to see if the level was gone. I only had a cheapie pregnancy test though. So they both came out positive. The cheapie says it detects 25 and that's more then 18. Then I went to buy a FR because my husband said maybe it's wrong. Well it showed positive right away and is much darker then the test I took last saturday. Am I losing my mind? Is there any hope? It feels like hcg of 18 was really low for 16dpo especially because the last time I miscarried it was 50 at that same time. Has anyone heard of this type of situation and had it work out? Sorry it's such a long post. I'm going to go crazy waiting until Wednesday to find out my levels