Hi I need help

Hi

I don't even really know where to start.
I've not spoken to people about my mental health before I was kinda brought up to believe that if you feel out of sorts you just have to suck it up and get on with things .
But after all these years I feel like I Just can't I've tried and I can't I feel anxious all the time when ever something is stressful or scary I think of the worst case senario and it goes around and around in my head for hours sometimes days .It effects most of my life I've even started to do certain things compulsively check doors are locked 3 or 4 times taking photos of it so if I worry later I can prove to myself that it is locked,touching light switches and certain things before I can leave it's not as much at home but at work .
I know that most people do these things but is this excessive I don't know ?
When it was just feeling nervous alot I wasn't worried but I'm older now I have a degree but can't bring myself to go for jobs I want cause I panic I get sick and my heart feels like it will implode it's like I'm there but I'm not ,like I'm underwater and I'm drowning so I run I've left interviews cause I just can't breath .
I don't know what to do I went to a doctor years ago and told her how I felt and shes said everyone gets nervous and I should just drink herbal tea ,I spoke to another doctor at the same practice and he said I should be grateful that I don't live in a war torn country that my problems were minor in comparison I felt so ashamed afterwards that I stoped talked about it .
I feel really alone and I need to know other people feel this way that I'm not a weak selfish person ,I have so many good things in my life someone who loves me and tries to understand,family,friends and I just want to be happy and enjoy theese things but I don't know where to start .
I'm sorry if theese sounds rambley it's 3.30am and I can't sleep I just wanted to see if anyone out there could offer me some advice .