Well as for the coloring you did about a month ago the dye was either not a good one, just fades fast or the makeup of the dye was too big for hair shaft. Not sure if molecules would be the right word but basically the color formula just sits on top of your hair.
As for the new dye, I would wait a bit longer (maybe another month). Give your hair a break. During that break give it some deep conditioning treaments, hot oil treatments, AKA plenty of love!
Then, re-dye. If you are doing a single color I don't see a problem with doing it home. Now if you want highlights go to a salon. It will cost more but it will be done right.
If you still want to do it yourself go to a place like Sally's and buy the dye and highlight stuff there. Get a semi color. This way you know it will wash out overtime if you don't like it and it is less damaging to your hair.
A few product suggestons from Sallys's that always worked for me when I dyed my hair at home:
Clairol Radiance Colorgloss- it has No ammonia, is a deposit only color (which means it won't lighten hair), adds shine, no guessing on what developer to use there is one made just for Radiance, 21 colors to pick from, no heat needed
Clairol Jazzing Sheer Haircolor- does not need a developer, very gentle on hair, use with heat for long results/without heat for temp results, adds shine, deposit only color, perfect for using with a highlighting kit
For doing at home highlighting I suggest using Kaleidocolors Tonal Powder Lightener - Neutral. It's great for hair from dark brown to blonde, it tones as it lightens, only takes 10 mintues to develope (less time if you just want faint highlights), can be used w/heat but for fainter highlights you use it w/out heat, comes in single application packettes. Use it woth a 10 developer for very faint highlights and 20 for more noticable highlights. I wouldn't go higher than 20 unless you know what you are doing.
