hey there and welcome to pc.
it sounds like you've been through a lot, and i wish you wouldnt be so hard on yourself. losing someone you care for is very difficult, and affects you very deeply. i read your post twice and it sounds to me like you are a person with a lot of promise. dont let go. please.
i went through a tough time too when i was a little younger than you, and i let it destroy my life. but you, you can make things happen.
i think you need to see a therapist or attend a support group. dont run away from your grief, or dull it with drugs and alcohol. it wont go away until you face it. and if the meds they had you on made you feel worse, maybe you could try something different. tell your doctor everything. speak up about where youve been and whats become of your life and get the help you need and deserve.
you are still so young. lets pull things together. you were a 4.0 student, i know you can pull off a 2.5. i have faith in you. hit the books and study like crazy.
and when things are looking down you remember youre not alone. we're here to listen. so get cracking!