Have you been pollinating the flowers? Just take a brush, Q-tip, or even a bare fingertip, and pick up some pollen from a flower on one plant, and transfer it to a flower on another plant. It usually works best when done early in the morning

Hi there. I had the same problems last year with my aubergines in the greenhouse. Pollination is the key. I left the greenhouse door open throughout the day and early evening to let more bugs in. I also placed a good flowreing plant or 2 (I used thyme and daisies) right outside the open door to attract more bugs to the open door. It seemed to work and all the other plants (toms and peppers) benefited too
good luck......

That was smart, Tim!