Rookie Shadow Priest going PvP

So I finally decided to hop into PvP scene after getting some decent gear and engineering. ( I'm actually against this but since everyone has it ) I'm aware that Spriest is top tier pvp class but somehow I really suck at it. The reason might be because I'm Alliance and everything is undead on my server.I have all pieces of Necrophile set, 2 of tier 0 warlock items ( head and belt ) felheart gloves and anathema. I'm gnomish engineer and cycling between Death ray, Shrink ray and Net-o-Matic with Insignia always equipped on cooldown. I'm typical shadow spec with improved vampiric embrace and inner fire. I have some really problematic match-ups but the general issue is ; I don't know what I'm doing generally.I panic and get out of shadowform to cast renew when I get shadow interrupted.Don't know how to answer an undead on first fear break.Not sure when to cast silence and mana burn.When to leave shadowform to heal.My most problematic match-ups are as follows ;Undead Rogue ; I trinket their kidney shot. Don't know what to do after fear break or when to leave shadowform.Hunter ; Try spamming r1 SWP to proc a blackout before being kited and mana drained to death.The abomination called Soul-link Warlock ; I straight up avoid this match-up and try to escape.Shaman ; I try to wand totems in between Earth Shock locks, but since I have no buffs on the CL and Earth Shock one shots me.Undead Priest ; Having to leave shadowform to remove that disease causes too much global cd and removes my mana while granting them a free mind blast mind flay combo.Need EVERY bit of advice to improve. Be it gear-wise talent-wise or play-wise I would honestly appreciate anything :) Thank you !