Mental Health issues with my beagle

Hello everyone, I am reaching out trying to seek some advice for my pet. I have had her since she was 2 and she is almost 9 now she does suffer from anxiety her whole life but now it has spiked like crazy. I have been stressing out on trying to find a solution to my issue. My beagle was never fearful of anything besides thunder and fireworks. Recently she has been super afraid of the sound of trucks and busses to the point where she did not want to walk outside at all, then over time it moved to her not wanting to go outside at all in the backyard too. I took her to the vet and they same maybe she's in pain somewhere in her neck or back and advised to get her a new harness. So I did, also we have been giving her Trazodone and Gabapentin daily but still nothing she does not want to go out to the backyard during the day. The way we do take her out is by carrying her physically out but rarely she'll pee on the floor too and also recently I have been putting diaper on her to see if anything I don't know. I also have noticed that in the morning when I get up I take her out her cage and I close it and when I tell her lets go out she goes fine like how she used to but after that no luck at all she'll hide in a corner or behind the door or run back to her cage so I have no idea what I'm doing wrong and if anyone has tips or advice I would much appreciate it. Thank you.