Two additional thoughts:

1) when you seat the tire's final bead on the rim, and prior to inflating the tube, work your way around both sides of the tire by squeezing in the sidewall and checking that no portion of the tube is trapped between the tire bead and the rim. Then inflate a bit until it's still squishy to your grip. Work your way around patiently with pressure, making sure to elminiate pinching. Inflate fully.

2) with the tire removed from the rim, run a cotton ball around the inside of the tire from both sides. It's possible that you've picked up a small steel wire from a car tire casing that has embedded itself into your tire, only to protrude inward. Too small to be seen, the snagged cotton threads will reveal the wire.

Good luck.

As others have said, patience and logic will reveal your problem. It may be as simple as too little tread, in which case, marking your tube's orientation with regard to rim/tire will help you pinpoint where the punctures are originating. PG