Nitrogen deficient

Im 18 days into flower indoors in soil, and getting the yellow leaves at the bottom which is nitrogen deficient as I understand? So do I give it more nitrogen while it is in flower. When I changed to flower of course the nitrogen was cut back. Do I add more or is this suppose to happen while in flower? Also some red stems. Im doing the 3 month cycle. Any advice appreciated. Thanks

if its just the bottom leaves i wouldnt do anything. if it spreads to the top of the plant a little then get some pics up asap so we can figure out whats going on

Thanks so much I will keep an eye on it.