HCG numbers decreasing :(

I'm an emotional mess. My HCG when the pregnancy was confirmed (last Friday) was 286. On monday, it was only 396 and today, instead of doubling, it went down to 340. The doctors office said I will most likely have a miscarriage. We've been trying for 18 months and this is the first confirmed pregnancy we've had. So I am a total mess right now. Just needed to post somewhere where others might understand the heartbreak I'm feeling right now. 😢💔