I have been running Google adwords campaign for the last 3 months. I have noticed that whenever I found a winning keywords, it will have good ROI for 24 hours, like 50%.conversion. After that, it will either get very expensive, almost double the original bid or I find that the conversions will tanked to about 20% which makes it unprofitable or even losing money. Still don't know why. Any AdWords experts here can jumped in and share some advice? Thanks.