Elaine, what you're feeling is completely natural.
It's no time at all since you lost your father, and my guess is that you went straight back to work, without giving yourself time to recover.
Could you take some time off now? You really need to give yourself a break, and come to terms with your loss. You have a stressful job, and it's difficult to cope when you're constantly on edge.
Could you talk to your manager and tell her how you feel? Please don't just carry on until you reach breaking point.
Love,