first of all I`m very sorry for your loss, it`s never easy to lose someone you love, especially a family member. of course I`m no expert in this field, but looks like you are going through depression, and to deal with depression we need to figure out what caused it. it may be you fathers death - you say you`ve dealt with the situation when it happened, but sometimes we think we "deal" with the situation by simply holding our emotions back, then the pain comes to the surface later and we can`t understand what`s the reason behind it.
the reason may be something else though - tiredness, irritation (something unpleasant may have happened you didn`t pay attention to, but it stayed in your subconsciousness), fear of future - like changing your career path...
in any case, the best remedy here is to be around people who care for you and support you. don`t push your boyfriend away, isolating yourself from others will only make things worse. try to explain to him how you feel, I`m sure he will understand and will help you to get through these rough times
all the best of luck and huge huge bear hugs for you!!!
Ani x