Faint line on clearblue then disappeared

I had a faint line on first response yesterday which is still there today then a very faint cross this morning on a clearblue, however it almost disappeared within 30 mins!!??  I'm so worried that I'm going to get my period. I was expecting it yesterday and didn't arrive. Altho Glow said I'm due today! So confused! Don't know what to think re the tests!! Clearblue this am pic attached. Any advice? Thanks x