First, I'm so sorry about the loss of your Dad. Was he ill? Was his death sudden or kind of expected? There's no easy way to get through such a loss, you have to allow yourself to go through the stages of grief, reaching out for support as needed, whether it be to your loved ones, or professionals in a therapy environment. Both is even better. Don't underestimate the power of a grief support group too. I recommend that to anyone dealing with a loss.
I admire your honesty and you admitting that you're self medicating. What kind of drugs are you abusing? Is this new for you or do you have a history of addiction? Obviously, that needs addressed in a big way. The sooner you start working on your recovery, the better, as addiction is a progressive disease that only gets worse. There are only three outcomes for addiction.....death, institutionalization (ie jail), or recovery. The outcome is in YOUR hands, you can do this.
I strongly advise you to seek out some addiction help ASAP. Depending on what you're abusing, you may need professional medical care to help you detox. Some substances are actually dangerous to come off without medical supervision (ie alcohol, benzodiazepines). Don't let fear of w/d hold you back, that's what holds so many addicts back. Of course it's unpleasant, but it's only temporary. It's a worth it trade off to feel lousy for a short time in order to get your life back and break the chains of addiction.
Please also check out our addiction community. I'm a regular poster there as well and I can tell you that the folks there are amazing. They will give you loads of info and support, 200% judgement free. Most of the members there have their own history of addiction, some with years of clean time, some with just hours, but they're all fighting the battle together. Addiction isn't a struggle meant to fight alone.
Here's the link to our Addiction forum:
Very best to you, please keep posting, and let us know how you're doing. We're here for you. Hang in there!!