"feeling better" is our physiological response to the medication working, not an indication of whatever you're sick with being out of your system. you could feel better but have bacteria remaining in small amounts not making you experience symptoms but then they begin proliferating. eventually, you'll feel sick again. take the entire regimen as recommended. it's only "recommended" because they can't make you do it, but really, you have to do it. that's how it's effective.