This sucks - big time - and I am so sorry!
If you have to be pissed, be pissed at the cancer and dig in deep and give it all you've got! (just like you thought was best for your Mom)

You have an awful lot on your plate - your mother, your father, your sister's death, your own struggles - that's too heavy a load for any one person to carry. If you haven't seen a counselor, please consider doing so. Your spirit needs some TLC, a chance to vent and the opportunity to mourn.

Be brave Kelli - you can make it through this!