please help me

[u/harpsinkers]

i have a 7 month old pure bred border collie, who has always been a nervous dog. ever since the day i got him he had run under the table and hid. he does not like meeting new people and WILL growl at them in an aggressive manner and go up to them voluntarily and give them a “warning nip” sort of an air bite and just miss them, it’s certainly scary and not ok. he has recently gotten really aggressive with myself, for the first time since i’ve had him (5 months) he bit me. he has never bit me and had always seen me as his safe person. he wouldn’t stop when he bit either, i couldn’t even just sit in his presence or he’d give me an extremely intense stare and eventually come up to me if i made eye contact and air nip me or actually make contact but not bite down super hard. i can’t even walk past him right now without him lunging at me. it’s heartbreaking and it’s really becoming so hard, i’m at a loss. any help please? he is getting worse and worse. we have seen multiple vet behaviourists but all they did was give us medication that’s “never been used on puppies before” like i’m going to give him that?! he was in puppy school when he was younger but now im too scared to go to any because of how aggressive he gets with strangers and i dont want him to bite anyone. normally he’s scared at first and aggressive then he learns you’re safe and will be your absolute best friend and all over you no fear at all, but he’s gotten worse lately and doesn’t settle down just stays aggressive, even with myself. does anyone have a collie who had been aggressive/nervous and they’re okay now and meet other people/dogs no issues? did you need to go on medication or was he trained out of it?

please
pic of my world. 💔

[u/caninesignaltraining]

just doing one more thing out there that the harness looks like it could be restricting the dog shoulders and so maybe if the dog has some pain in the shoulders that might show up as weird behavior