Help! Bfp then a bfn


I was wondering if anyone could send me some insight as to what is going on. Last night I took a pregnancy test and got a bfp. The second line was faint, but definitely there. I have also been taking my bbt. This mornings bbt had dropped and the pregnancy test I took today gave me a bfn. My husband and I have been ttc for about 4yrs now. I do have pcos, but have been getting regular periods since starting metform 3yrs ago and also have been taking clomid. We were both so happy and over the moon that I got a bfp, we would hate for it to not be true. The top picture is the test I took last night and the bottom one is from today