depression!!! urgent!

I think im going through depression for the 4 th time in my life..actually to be truthfull i think ive just been depressed for two years now but its getting more serious.

Along with other symptomes of depression I have really bad OCD too. They are not the same OCD i had before but different ones.

My main concern is...well...im constantly thinking about death. Not sucicide but when i watch the news and bad things come up etc etc i think that either i am in that position or my family members.

Recently, for the last 2 months, when i drive i vision that i crash my car and die or my son dies.
I have a fear of planes and imagine/vision me and my family laughing and having fun on a plane and then the plane starts to drop and all i see myself doing is holding my children for dear life and thinking how must my children be feeling...immediatly after focusing on real life again i think to myself would my children feel death if we were to crash, would they be scared or would it just happen too quickly for them to notice. I do this with not only my children but with my husband or other family members.

I am obsessed with thinking about people dieing when they are very much alive and well. I not only think of death but obsessively think about what would happen if someone dies and things like if i were to die how will my children cope and would my husband marry again. Ive even recently discussed death and other facts of life with my 6 year old son. I didnt say it in a bad way but explained to him that god made us therefore one day he takes us back. He got really upset. But i just wanted him to be prepared cos im always thinking that im going to die in the next second.

I wish i could control my thoughts. However its not the thoughts that affect me, its the flash of visions that i see played infront of my eyes.

Theres more to my depression and i defo know that its depression because ive had these visions 4 years back when i was diagnosed with mild depression. However it took me 1 and half years to manage to control it by putting a stop to watching the news channels so i dont hear of plane crashes and terrorist attacks etc etc.

I would like peace of mind so if someone could help me i would be very much grateful.

Theres a herbal remedy called St Johns Wart, is it good and does it work? What are its side affects?
Any other herbal remedies that i can get from loacl shops. I am from England.

I love my family to bits and i want to be free from these horibble thoughts. Im always hiding my feelings from my husband because i always moan about other things i dont want him to think that im lying or just trying to get attention and the main thing is he is very busy with plans to give me and my children a better future.