it takes me FOREVER to make the slightest gains in strength+size

so anything that makes me lose weight gets me worried heheh
so i've been doing a good deal of cardio the past month and i've already lost 6 lbs., i was only doing it to get my abs to show, havent lost any strength yet but at this rate i think im gonna start losing muscle soon
how do i know how much is the right amt of cardio.
thanks