Thank you for your question it is a really interesting one.
Everything you ingest or inhale or absorb through your skin has the potential to harm you so please make sure that you get advice from your GP or a qualified complementary therapist before you try anything new and if you suffer any reactions please get medical advice.
The essential oils that are most widely used for stress are:
Lemon and Orange and Lemongrass
Try chamomile tea and green tea (stay away from caffeine)
There is some evidence that some of the below are effective but please be very careful especially if you are on any other medication and check with your GP BEFORE taking them. Do some homework on them yourself ad look at the studies and the claims they make:
Vit B complex and Magnesium
Generally having a good diet with lots of fresh vegetables and fruit and limiting caffeine and alcohol will affect your mood and your stress levels so monitor what you are eating in a diary and measure your stress levels to see what affects it.
Your question about chewing is also interesting and I think that in the long term the answer is to wean yourself off the habit as it can add to your stress and give you digestive problems but in the short term consider chewing natural products such as liquorice root or ginger. I also had a look online and there is a natural chewing gum on the market called Chewsy http://chewsygum.co.uk/
so you could give this a try as it might make you feel less guilty! You sound like you might need some professional help to kick this habit so please talk to your GP about it or refer yourself for some counselling.
I hope you found this helpful and I wish you all the best.