I can’t orgasm from oral sex

Ok I have never been able to orgasm from oral sex - only from direct clit stimulation and this was only with my ex

I am now seeing this new guy and getting into oral sex again (would not do it with my ex because I didn’t like it but now I do again ?!) and I cannot for the life of me orgasm

Part of the problem is that so far I have needed my legs to be very straight and tensed to orgasm and that’s not a position I can achieve while receiving oral

Any advice ?