I am sorry to hear that you suffer with both physical and emotional challenges and that you tend to get very nervous in certain situations.
Getting to the source of the stress is usually key to starting to change how we feel. Are you aware of what the situations have in common that make you feel nervous? For example, have you had a difficult experience in the past, which knocked your confidence?
Without knowing much about your situation, it is hard to recommend what may help. If this pattern is repeating and causing you stress regularly, it might be helpful to seek the support of a counsellor, life coach, NLP practitioner or hypnotherapist.
Any of these methods would aim to identify the source of the anxiety and find ways to help you overcome the fear.
You could also perhaps consult with a Medical Herbalist who would be able to talk to you in depth and prescribe a treatment plan to suit both your physical and emotional challenges. (www.nimh.org.uk)
Finally, you might like to consider taking a Flower Essence. Flower essences are safe to use with other medicines. They work to restore emotional balance when times have been challenging. I would suggest that Confidence essence may be useful since it can assist in overcoming issues from the past which have knocked our confidence.
I hope this will give you some avenues to explore and do hope things get easier for you soon.