What oil paints are you using?

They are not all the same. The less expensive brands have very coarse pigment and there is nothing you can do about it - they will be lumpy on a 1/35 scale face. I use Windsor Newton as they have the finest grain I have found. I mix flesh using Titanium White, Burnt Sienna, Cad Yellow and Cad Red. Buy yourself a few of small tubes (they are expensive) and give it a try.

Also, I basecoat with Floquil Flesh lightened with about 25% Reefer White. The oil paints I apply almost as glazes thinned on the brush with linseed oil. The advantage to using Floquil is if you screw up on the oils, you can wash them off with turpentine and start over without hurting the basecoat.

Good luck!