leaves yellowing and falling off need help

alright over the last 3 days i have noticed at least 3 different leaves the were near the bottom of the plant and dont know what the issue is. one of the leaves when i touched it fell off i am in the beginning of the budding stage i have also seen a lot of newer foliage coming in so i don know if this is normal or not

bump, i decided to remove all of the yellow leaves on my plant besides the one in the 3rd picture.

you've got a nitrogen deficiency buddy. Whatever grow nutrients you were using for the veg stage, add them to your feeding schedule for another two weeks at 25% of the recommended concentration and you should be okay. Don't do it for more than 2 weeks tho!