pregnancy test

Has anyone had false negatives before with those cheap eBay pregnancy tests? I'm 13dpo, on day 37 of my cycle, my cycle only usually lasts for 28-30 days and I'm never late. Ive done a couple of those tests as I've been getting a few symptoms such as feeling nauseous, fatigue, hot flushes, dizziness (to the point my eyes go fuzzy and everything goes dark) headaches, slight loss of appetite, and stomach cramps. It's a 10ml test, is it too early to tell maybe? Or maybe I'm just unwell and over thinking? I've had a chemical pregnancy before, Earlier this year in January. I am due to have a pelvic and abdominal scan for abnormal pain so maybe my symptoms could be linked? Your thoughts and advice would be helpful and reassuring ladies, before I see my GP. Thank you