I'm a girl and get a similar thing! I really try and focus on engaging my chest but it never seems to ache like my arms.
It could just be a case that your pecs aren't being worked as much as your triceps during your workout because your triceps are smaller muscles and need to work harder to manage the weights.
Like you said, the other possibility is form. Best advice is before you start a movement, think about where it's coming from. So brace your core and chest, and you know the 'mind to muscle connection' people talk about? Imagine the movement coming from your body not just your arms. So taking the chest press for example, don't just straighten your arm but think about squeezing your pecs, then your triceps and biceps then push the weight away.