3 weeks bfing and still hurts!

Ash
So I've been bfing my 3 week old this entire time and I thought we were finally getting the hang of it, but the last 2 days he has gone back to latching too quickly and biting me with his gums. I know how to latch properly, but he's so eager to eat that he doesn't give me a chance. 
 At his 2 week appt he hadn't gained much weight back (lost 6 oz after the hospital), so I'm very anxious about him getting enough milk and being diligent about feeding every 2 hours. Problem is, my nipples are so red and painful from his bad latch. I want to call a LC  tomorrow. Im so frustrated. 😭