This is so frustrating!!

My husband and I have been TTC for almost 5 years. We have been to the docs soooo many times. Tons of test and retesting and everything is always just fine. So I was supposed to start my period on the 5th. I didn't even realize I was late til the 7th. I'm very regular so I was like ok I'm guna test in the morning. So I do. I look down a couple mins later and see a faint line! Iv never had this happen! So every morning when I got up I took a test. Each morning it gradually got darker and brighter! Then 7 days of positive test the next morning it's a super faint line! It was a different test but when I looked at the sensitivity they were the same. Iv had a few early miscarriages or chemical pregnancies but iv never had a positive test at home. Iv always found out at the docs because I would have a weird pain or something weird come out of no where a couple weeks after my period so I didn't even think I was pregnant but it always ended literally a day or two after finding out. It's crazy how I can have a super positive test one day and the next it all disappear! Wtf is going on? Why do I keep having this happen? Docs just tell me it's unexplainable infertility