it's the first time I'm growing a plant, I'm currently on the 7th week of flowering, is that normal if my leaves are turning yellow or is that a ph problem ?
Looks like slight nutrient burn to me.
Lower the feeds and ensure its getting a well balanced fertilizer Micros and Macros in combination with PH. EC works well as a baseline to operate off of.
Good Luck!
Plant looks over fed and with developing magnesium deficiency.
But at this late stage it will be impossible to "fix" anything.
One random picture and no diary ain't much help either.
It could be from a pH fluctuation, it could be the beginning of normal fade if you're approaching the later stages of flower. More info/a diary would be helpful. Check your runoff pH to see if your rootzone is out of range.