Auto invest or wait…

I need help, i get paid on the 5th every month. Every month on the 5th, i log into trading 212 to invest £500, into my S&S isa, the problem is that it seems like every month on the 5th, the market is up ! And then the week after or a few days later, its back down, am i wasting money by investing when my accounts at the highest its every been, just to add £500 into and in another week its like i only put £350 in !, i know the saying its about time in the market, not about timing the market, a lot of people seem to auto invest and don’t bother looking at it, probably for this same reason !! But i enjoy doing it myself i feel better about myself knowing I’m stepping closer to my goal, compared to just watching money leave my account, Its all psychological but i enjoy it, its never bothered me before really but i just feel if i wait another 2 days instead of doing it now, i can buy in at a lower rate, not at my ALL TIME HIGH !, any advice is appreciated and any criticism is welcome !