I am also on my first grow, going 4th week of flowering. One thing I learn is...
I do to many unnecessary stuff, and I worried too much about little things. Which will drive you nuts. Imagine a dog trying to chase it tail.
First off, relax and look at the canopy for issue. Most of the time the bottom leaves will change color or die off or act up because, #1- they don't have enough lights or light at all, #2- they get nutes burn because they are closer to the roots, #3- the top of the plant is draining the nutes from the bottom plant, #4- the plant doesn't care much because it worry about growing and not what is left underneath as much.
Print out a chart that has image of the cannabis leaf with different symptoms. Next time add more picture and make sure to include the plant and better if the leaves are still intact because once you take it off, it only take second before it start to wilt and die and look worst than it actually is.
I have been in your shoe and still am. First timer are always on their toes... which isn't a bad thing.