First, let me remind you that there is really very little difference between a conventional medication and a herbal one. When using either of them, you need to consider that both can have unwanted side-effects, both have contraindications, interactions with other herbs/drugs etc. One is not necessarily safer than the other.

I strongly suggest you consult a professional herbalist. Which does NOT mean a person standing on the other side of a serving counter handing out commercially-produced bottles of this and that! As with conventional medication, you need a herb and a dosage that suits YOU!

The usual dosage for Valerian is: 300-500mg in capsule or tablet form one hour before bedtime for insomnia. 30g root per 600ml water as infusion. Take up to 3 cups per day. Tincture: 5ml taken before bedtime.

Warning: Unpleasant side-effects (headaches, muscular spasms and palpitations) can occur with long-term use or with excessive doses. In extreme cases, it has been known to cause coma or even death. Poisoning may result if large amounts of the tea are taken for more than 2-3 weeks. Do not boil the root. Consuming large amounts of valerian may cause headache, giddiness, blurred vision, restlessness, nausea. It can act as a narcotic in large doses and can become addictive. Seek expert advice before using and use ONLY under expert supervision.
I suspect that Valerian is not the herb you need for your anxiety and stress. I doubt it will do you any favours. Before you start popping pills (herbal or otherwise) consider other aspects of your life. Are you eating a good, healthy, balanced diet? Are you getting enough physical exercise? Are you getting enough natural sunlight on your skin? All these things (or lack of them) can affect both your mind and your body.

Perhaps you could discuss with a herbalist safer and gentler herbs such as Hops, or Scullcap, or Catnip, or Passionflower, or Rose, or Lavender, or Chamomile.

If using Lavender, drink a cup of the tea every second day, but you can always use it (fresh, dried or the essential oil) as aromatherapy.

Try to increase your intake of calcium, magnesium, phosphorus and potassium. These are valuable minerals that can be depleted by stress. (Foods high in these minerals include Apricots, Asparagus, Avocados, Bananas, Broccoli, brewer's yeast, Brown Rice, dried Fruits, Figs, Fish (especially salmon), Garlic, green leafy vegetables, legumes, raw nuts and seeds, Soy products, whole grains, and yoghurt.

Avoid foods that contain caffeine such as coffee, strong tea, chocolate, colas and other soft drinks that contain caffeine.

You could also take vitamin B6 and thiamine daily.

I sympathise with your situation. For 10 years I worked a full-time job, raised 2 children, and spent my evenings as a student at university. In between times, I had housework/lawn-mowing, and assignments and parental duties to attend to. I know how hard it can be. I survived on an average of 3-4 hours of sleep per night - but I think what kept me going was eating properly, and keeping physically active.

It's part lifestyle:
1 - Cut down on the soft drinks, coffee, tea, etc. More fresh fruit and vegggies, less junk food.

2 - Get outside and walk for at least half an hour a day. Even better is a hard workout once a day. (the time you spend working out will make it easier to study, and de-stress you)

3 - study outside in the sunshine if you can.

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Then the herbal ... see link.

Here is a link that might be useful: Herbal sleep aids

All above sounds good. My experience for what it's worth:
I use valerian root tincture occasionally to help me sleep.
Only for a few nights when I'm having trouble. Then I lay off of it. I never take a high dose of an herb, and never the same one every day for more than two weeks without taking a two week break.
The valerian tincture has worked like a charm when I needed it. Only problem I had : The smell!!! Tried to make a decoction of root, it stunk up the whole house. Tincture, not so bad.