Hi there, I've been swimming more than regularly during my holiday break.
Recently I realised I have this physical problem which has been bothering me ever since I feel its getting a bit out of hand.

Every time I do my drills and sets, after a few times, I get this Nauseous feeling, a lil giddy over the head and the urge to start to vomit(not yet).

And whenever I do my 100 backstroke times, I'll get MAJOR numbness/cramps? on one of me legs. And I'll feel super numb from my thigh onwards, up to my toes. My movements would be restricted as soon as I get up from the water.

I've read many tips from various forums and articles.
I drank Orange/Apple Juice 30mins before I hit the pool.
I start having a more regular sleep times and meal times.

It did improve a little (not significant, but I can feel the difference)

Is there anything that I can do to improve this situation?

P.S
On a side note, ( I dont wanna make multiple threads just to ask this)
Is it too much to swim 5 times a week 3 hours per session?
Intensity is moderate.

Cut down on the hours per session

That means that you are working out hard. When people work out, they may get light headed and want to vomit.

Like sandyhoshuying said, my suggestion is that you cut down on the amount of time and the intensity at which you swim and build it up slowly instead.

What the above two posters said. Despite what your mother says, don't go into a workout with an empty stomach. Also, this probably means you are out of shape. That routine is probably close to what many college swimmers undertake...if you're not in seriously good shape, you're overdoing it.