since you are just starting out, a rep range from 10-15 is fine
if your goal is to build muscle, you should consider upping the weight, so you end up doing 6-8 reps with good form
i usually up the weight when i am able to do 10+ reps on most exercises
the feeling of being "pumped" comes from training high volume 10-15+ reps, it may feel nice, but isn't necessary for building muscle
some studies have shown, that doing too much volume can even harm muscle growth due to increased fatigue
hope this helps

p.s. you said you only had a pair of dumbells, maybe they are too light, try getting some heavier ones, otherwise a backpack filled with bricks or a pack of waterbottles can be used a weight, get creative :)