Faint BFP frer BFN CB digital

Very faint positive 11dpo frer. Negative CB digital. I had exactly the same last month first faint positive 11dpo then my frer and CB regular got slightly stronger and then after a week went negative. I never got a positive digital. Doctor said was chemical pregnancy. Worried it's going to happen again. And even more worried that actually I've never had a positive and just imagining...