Problems with ejaculation and staying aroused.

I have recently encountered a problem with in the last month or two. I don't have any problem getting aroused or "Hard" I just have a problem staying hard as well as ejaculation. Before this problem I was haunted by premature ejaculation or quickly reaching the point of ejaculation and now I have been having problems reaching ejaculation with vaginal sex, oral sex, hand jobs and even masturbation. I have to completely concentrate to be able to achieve this within 30 minutes. I have never had this problem before and it is beginning to damage my sexual relationship with my girlfriend. She has multiple orgasms and feels as if she isn't enough sexually for me. I also have problems staying erect during sex. When my penis is outside of the vagina while changing positions, I loose some of the hardness. Does this seem like any medical problem or am I just extremely nervous. I never had this problem until after my break up with my last girlfriend.