This could be caused by a lot of things.
You could be drinking a lot of alcohol or caffeinated drinks, anything your body tries to flush out, leading to a drier throat.
Tobacco, drugs etc. can change a voice, obviously.
You might not be getting enough fluid.
You may have swallowed a porcupine (probably not, tho)
The one I find happens most often is neglecting the physicality of singing. It involves a lot of muscles which need to be exercised to be strong.
Here are a few general tips for keeping the warmer tones in your voice.
If you're focussing on hitting those high notes "out of the blue" without some kind of warm up, that's probably straining your voice, which can lose some of the warmer low-mid frequencies and make your voice sound husky or scratchy.
If you're trying to get to higher notes without supporting them with a lot of air from your lungs, that can over work the vocal cords to a similar effect.
Always warm up your voice, practice breathing deeply filling your lungs. You can exercise your diaphragm with repeated "ha" sounds (with or without an actual note, this could just be with breath).
In rehearsal, never keep singing when your voice starts to feel sore. Repeatedly singing through a rough voice can cause some real long term damage. (When it comes to performance, you need to make a judgement about how important it is and the risk of losing your voice for a while afterwards).
Importantly, you really do need to project, with or without a microphone. Don't rely on technology to compensate if you're not using the singing muscles to their full effect. A good guideline is to sing into a microphone as though you're singing to someone on the other side of an empty room. (This both improves your tone and helps to avoid some of the problems above).
These may not all apply to you, but the bottom line is always the same. Take care of your voice, and treat it like a muscle, exercise it regularly.
Hope this helps.