Help with possibly too strong glasses?

I have an issue and i would like someone else to weigh in. I'll still probably get an independent eye exam but the wait time is really long. 

I've always been short sighted since a kid. Recently i went to my optometrist to get a a new pair bc my old glasses got damaged. Got the 1 or 2 test and a new rx while i was there bc its been 2+ years since my last one. I had smth like L-5.5 and P-5.0 on both eyes and while my right eye went up to -6 she claimed my left one went all the way up to -7. She strongly suggested diabetes, which i dont have and i have the lab results to prove it. She was really rude/pushy abt it. She said smth like 'everybody always claims their prescription is not that high' and overall was very snarky. Shes why i dont like getting my eyes checked lol 

So i got the glasses and i feel like theyre bad? Like my left eye is constantly strained and red in the inner corner, esp if i look far away like driving for multiple hrs. In mid distance (projector in class) i can see ok with my right eye but i cant focus my left eye for nothing. I have my old rx contact lenses i sometimes wear which are -5.25/-5.5 and i feel that while theyre slightly too weak i can read text better/more confortably than in the glasses. When i change back from them to glasses i often get a headache. People say im constantly squinting the left eye in glasses too

Is is possible my left eye is too strong? It's been bothering me a lot recently bc i wore the contacts a lot and felt much better

Sorry for the long post I don't know how to explain it properly in a short manner