Hi everybody !
To say I'm struggling is an understatement.
For the background, I'm a woman and I weighed 90 kilos (200lbs) at my highest, and I lost it all without any help, making a few mistakes during the process (by cutting calories a lot, until I was down to 500/800 kcal a day, but at the time it worked like a charm). I reached a weight I consider healthy and normal at 63/65kg(140/144lbs) for a 1m67 (5'5.75). I've also gained muscle in the process. I've been maintaining that for 7 years (I think?). I've never gained any weight back, apart from a few variations of 5kilos, which I consider normal. However, I'm having a hell of a time getting down below that, and yes, I've still got some fat to lose, clearly.
By some miracle two years ago I managed to get down to 57kg (126lbs) and I still had a few kilos of fat I wanted to lose (and I was also more muscular at the time). Ideally, I'd like to be at 20% fat, which I think I'll be able to achieve if I get to 55kg (122lbs).
Today I'm 65kg (144lbs) and I've been back on a very strict diet and a fairly intense workout program for 50 days and I'm stagnating stagnating stagnating. I must have lost maybe 300 grams...
I have an office job, I'm a web developer, I sit on my *kitten* literally all day lol, so unfortunately, really, inactive. (but I go there by bike which is 40 min a day), I'm a woman, not very tall, with a very slow metabolism, and with time, I figured out that 1700/1800 was my maintenance.
I'm currently at 1300/1400kcal per day, I work out 6 times a week:
-3 full cardio sessions of 1 hour (and it's relatively intense, I'm at 170 bpm the whole time)
-2 full strength training sessions (I started strength training 3 years ago and even though I've been moderately assiduous, I don't want to lose everything I've spent so much time building up, so I'm obliged to maintain strength training sessions to keep a bit of muscle mass)
- and one "mixed" session (moderate cardio and full-body strength training).
And I also try to do at least 5,000 steps a day on top of everything else.
And I don't lose a thing. I've been counting my calories since I started my diet, which was 10 years ago, so I'm familiar with it, I count absolutely every ingredient and weigh everything. I cook all my meals, never eat out, no processed food. So this counting calorie thing is as reliable as it gets. The problem doesn't come from that.
At this point I don't know what to do... it's so frustrating and discouraging. If I ever miss a day at the gym (because I'm too tired or I've got my period, for example), I feel guilty all day because it will slow down the already painfully slow process even more.
Sorry for the long post, I don't know how to keep it short lol. And thank you to those who will take the time to read and maybe reply too!

PS: I've already done low carb, keto, fasting, omad and omad + keto (worst thing I've ever done, clearly not for me) and none of it has had any significant results. I understand that it can work for some people, but that's not my case. And I don't want to have to make my diet even more rigid - it's complicated enough as it is to stay at 1400kcal a day and I'd like to still have a little pleasure in eating and not restrict absolutely everything that brings me a little joy (i.e. fruits and a square of dark chocolate).