TMI! TMI! TMI!

My husband and I have been ttc but not all gun blazing about. *We welcome it if we're blessed with it* I've kept pretty well track of my menstruation cycles pretty well and I KNOW I wouldn't have gone this long without a cycle. Stress has been a lingering factor but not enough to throw me off this much. Thyroid and liver function came back great and healthy. My last menstruation was 7/19-24. But all tests have been negative. However, I noticed this 9/4. Could it be implantation bleeding? There's quite a bit of CM. Help?