Stagnating seedlings

After a flying start with fast germination I steadily pricked out seedlings of aubergines,  peppers,  chillies & tomatoes as the first true leaves appeared and while I expect everything to stop for a while I've realised that nothing is really growing on.
Most aubergines, pricked out in early March still only have a single pair of tiny leaves.  They have been indoors in the warm until about 10 days ago.  I know they were initially too dry, as I over-compensated for last year's fungus gnats,  but that was quickly rectified. 
I'm guessing the cheap compost is the problem,  do you think it's worth buying some better compost and repotting everything?  It all has to go in the ground by mid May as we'll be away then, so one month's time.
Thanks all.