I was in the same boat as you but my test WAS low (like half of yours) and getting that fixed led to results. Turns out I was doing everything mostly right for several years, though I did spend some time before that before figuring shit out. I think I have things nailed down pretty well now, to the point where I can go through bulk and cutting phases and am consistently improving my physique. Whereas before I could go from fat to skinnyfat and back and forth, maybe making a bit of gains overall (but never in the chest lol)
I think the issue is you are not tracking your macros. You're talking about the training you do, your weight gains and losses, and you went as far as getting a blood test. However you didn't mention anywhere what your caloric intake and macros looked like.
My recommendation: Use
this TDEE calculator and eat at a +500 calorie surplus. Try to get roughly 0.8-1g of protein per lb of bodyweight each day, fill out the rest with carbs and fat.
WEIGH EVERYTHING YOU EAT AND TRACK YOUR MACROS AND CALORIES. Do this for a few months at least, to get an idea of what it takes to reach your goals. Eventually it can become more automatic, but even then you really have to watch what you eat.
I GUARANTEE that you aren't eating as much as you think you are when trying to bulk. Especially considering how easy it seems to be for you to cut.
For training I'd recommend a 4 day or 5 day program focused on hypertrophy. I had a lot of success
with this one. I have combined it with 5/3/1 for strength, and combined it with GVT for pure hypertrophy.
One last thing to consider, if you aren't progressing in some way
every single week for your first few years of lifting, either increasing the weight or increasing the reps, you are doing something wrong. You aren't eating enough and/or getting enough sleep. There's practically no way you should be bench pressing exactly the same weight/sets/reps that you did a week or two ago. Something (weight/reps) has to progress constantly, or you are spinning your wheels. For big compound lifts, weight should go up. For smaller muscles like delt raises, focus more on increasing reps. Because it's easy for other muscles to take over on those lifts, and your progress will be 'fake'