I still have days where I feel insecure in the gym. A lot of days actually. I am not immune to it. Days where none of my clothes fit. Days where I feel scrawny and not strong. Days where I look in the mirror and look at my legs and don't feel fit or in shape. Days where my emotions got the better of me and I wanted to cry halfway through my workout. I've learned a few things about myself.
1) It is normal to have days where you feel like this. Hormones (time of month), sleep, and nutrition all play a big role in these feelings. Making a conscious effort to take care of yourself the next day or two is important. Schedule sleep. Recognize that your hormones might just be on high alert right now. Really focus on feeding your body nutritious foods. All these things matter.
2) Do not quit. It is okay to feel this way sometimes. Everyone does. You only get stronger and better by staying. If you need to do lower weight or lower intensity that's okay, but keep going. Don't quit. Don't leave. Finish your workout. (This is the mantra I tell myself).
3) Remind yourself: the actions you set in place today will determine your future results. Small decisions each day make a big difference over time. If you tear off one paper towel at a time you don't notice an immediate difference. But over time, each day, that paper towel rung starts getting smaller. Small changes each day = big results in the end.
4) Be kind to yourself. Tearing yourself down in the mirror never did anyone any good. Even if it feels cheesy, look in the mirror and actually think the words to yourself. Say something kind. Recognize how good your ______ looks. Congratulate yourself. Being kind to yourself goes much, much further than being vicious ever does. Give yourself permission to make mistakes, dust your knees off, remember your goals, and press forward.
I am right there with you some days. I struggle too. We've got this.