Hi,
Relationships with colleagues are always tricky and you are definitely not alone in finding this hard.
Can I suggest that you watch the TED talk by Phillippa on this website and then look through the information and books that this company have written?
www.4dhumanbeing.com I think you will find the advice really interesting and useful.
Practice what you are going to say to your colleagues before you speak to them and go over what they might reply, write it down if it helps this will give you more confidence when you do approach them.
It's easy sometimes with work colleagues to just see them as their work role, it's really helpful to try and see beyond their job title and connect with them as fellow human beings. See if you can find common ground, hobbies or interests to discuss. Also maybe help to organise some training in communication skills etc as these are often lead by trainers who can get barriers broken down.
You might find that some counselling would help you become more confident as it will give you some tools and techniques to use in social situations so have a look on this website
www.bacp.co.uk for a counsellor who can help near you or speak to your GP.
I hope you find some of this useful and I wish you all the best.