Dildo only goes in after sex?

I always have issues putting my dildo in. I use lube…lots of it. I slow down and take my time yet it never goes in. After having sex a couple nights ago, I thought it’d be the perfect time since my vagina would be dilated already and it just went in so easily and smoothly. Why can’t I do this without having sex first lol?? I feel like a virgin all over again trying to insert it