Ive been using the same style needles as Vince. Try holding the vial of Testosterone in your hand for about 5 minutes before drawing it up. Warming it seems to help speed up the process for me, in both drawing and injecting.
I received my new injector device and used it last night. It works GREAT the injection didn't hurt at all. Injected into the upper leg with a 23g 1 1/2 needle. aspirated and everything just fine. I would highly recommend this device if you have needle phobia. Or have a hard time injecting yourself. https://unionmedico.com/90-super-grip/ You can get different colors than the one pictured. I got black.
Warming the oil will help dramatically, from taking a (capped) syringe between your lips for a few minutes to running it under warm water, warming will help it flow.