my 1st plant ever seems to dieing :(

so i got this plant. its only one plant and its my 1st atempt. baiscly my mate gave it to me becouse his girlfriend kept moaning at him, its been in his garden all its life. he literaly threw a seed in a pot of soil outside and it grew!
so anyway, i got it in my wardrobe now under 125w fluresant light, got myself some nutriants and a ph kit. the ph level after adjustment is between 6.0 and 6.5, as was suggested by the person i got the kit from.
the temp in the wardrobe is 78f give or take. its hard to control the temp and im not adding any extra heat.
i been reading advice on here and how its done but im still doing something wrong!
i had it for about 3 weeks now and the plant loved the new light and doubled in size, great right? i thought so aswell....
but now it seems to be dieing. all the leaves are going or gone brown, even the new leaves!
i have spent atleast an hour checking for bugs, there is none. i moved the light further away and lowered the dose of nuts i was giving but it seems to excelerating! now, this is just an experiment to see if i can get anything from it, before i get myself a tent. im aware it wont have much yeild.

can someone help?

You need to re-pot that plant asap. That's why it's growing like a pine tree.

I like your wall reflectors btw.

thanks. what sized pot would you recommend? and any advice on how to do it?

You'll need a pot big enough to complete the entire flowering process in as transplanting during flowering is best avoided whenever possible. There are genetic factors affecting root growth but in general you should base pot size on flowering time. Five gallon buckets support at least 80 days of flowering and are a common flowering pot size. They can make it through the flowering cycle of all but 100+ day Haze strains. I wouldn't reccomend anything smaller than 3 gallon. Once you get to know your strain, you'll know how long it needs to flower and how much room it needs in the pot to finish without becoming root bound.

Transplanting during flowering must be done as gently as possible to prevent shocking the plant. It's usually easier to remove the root ball from the current pot when it's dry. It's not as heavy and with most soil mixes, won't break apart as easily. Always wet soil until a handful drips a few drops of water when moderately squeezed. Fill the new bucket with the soil just enough so that when you place the root ball on top, the top of the root ball is level with the top of the bucket or just an inch above (it will settle to a lower height). Don't press new soil down, always tap the container on the counter to settle the mixture. Pressing it down can compact it too much, preventing air from reaching the roots. Add new soil around the edges, tap the container and water lightly.

ok thats great, thanks. have you any idea from looking at that plant, what stage its at? i know its a female and its getting smelly and sticky.

The new light could have accelerated growth, causing it to outgrow the container faster. You say you've had it for 3 weeks. How long have you been flowering? It's hard to say where it's at without closeups up bud formations.

i pretty much put it on a 12 hour cycle from the start

Guys i need some help. I done as you said i put it in a huge bucket, some top quality medium, i put a litre of clay balls at the bottom for dranage. But the leafs are still dieing and the new leafs only have like 3 prongs. That kinda tells me its not happy.
I had the plant for a couple of months not but even in the new pot, it dosnt seem to be doing much. I had it on 12 hour light cycle as soon as i got, you seen the pics, its not changed much atol. This is only an experiment.
What i want to know is, will it hurt to put the plant back into veg stage? 18 hours of light?
I need it to fill out and get some decent sized leaves. This plant is doing nothing except producing crap new leaves that are going brown aswell as the rest of them. Im keeping it aluve, just. Any advice would be great!! Thanks

New pics would help but it sounds like you need to feed her.

ok here are some pics. the bucket is 4 gallon. i added the best medium the shop had to offer. i have givin it no nuts (i use soil bloom) as the person in the shop said the soil had enough food to last it for 2 weeks. so i can start feeding again this coming week.
its just not doing anything. i took the best close ups i could get and they are HDR.

as you can see alot of browining leaves, the leaves are tiny aswell. its in a simalr state through out the plant.

should i keep it in flowering stage or is it safe to put it back in to veg stage for a few weeks?

so i should start feeding then?