I want to do a multiple regression , correlating offspring produced on mating one with offspring produced on mating two also with male age at the first mating as a variable. SO the 'dependent' variable would be offspring produced after second mating with offspring produced from first amting and male age at first mating as the other two (explanatory) variables.

There are over a hundres repeat measures of offspring counted for each mating. But only three different male ages 4days, thirteen days and one day old.

I was using SPSS for glm's then did stepwise in R, with many other variables, now im looking at multiple regression and nothing makes sense to me, i know what i want to do but not sure how?

Do i -> analyse ->regression -> linear ,then put both first mating offspring and male age in the independent box? Not sure what stats / plot to look at?