First time using compound, med kept getting pushed back to the vial!

After doing 4 weeks of Zepbound 2.5 and 8 weeks of Zepbound 5.0 and since the cost was too high, I decided to start using Tirz. Placed an order from Lavender Sky (Hallandale pharmacy) and did my first injection on Monday (I was so scared of using the needle just a FYI). Pulled 70 into the syringe, then noticed while I am pulling 70, when it gets to the 70 mark on the syringe, something (air maybe?) pushes the medicine back into the vial so I had to keep pulling more. Is that normal? Not sure what I did wrong. Finally, I grabbed a chunk of fat on my stomach and slowly injected myself. It did not bleed but the injection site was hurting afterward, also, is that normal?
Since I upped the dosage from Zep 5.0 (equal to 50 in Tirz), I expected to have the same nausea side effects as when I first dosed up from Zep 2.5 to 5.0 but it was not like that at all. So, is that normal?
Looking forward to hear from other users here to see if I did things correctly and what I can do to make the next experience better. Thank you in advance