Should I be worried about my weight change?

So between June (when I finished my exams) and now, I (18f) gradually put on about 6 pounds over and I don’t really know why. So I did have a fair few celebration meals and holidays, not a huge increase on my previous eating but I’ve worried a bit less about healthy eating over the summer. But I’ve also trained for a half marathon and done some weights so not sure if some of the new weight is muscle? Also my stress level has gone 100 to 0, maybe that’s something to do with it?
I haven’t been very concerned about the weight, though when I weighed myself the other day and saw it had gone up again I began thinking I should be worried. I feel healthy and energetic, I don’t think I look any chubbier, and I'm well within my BMI still. I don't really know what to do now, other than just try eat healthy and not worry about it. I'm also about to start uni, not sure this is a good time for a weight loss plan/ diet. Anyone been in a similar situation? Any advice? Tysm for reading this c:

This could be a host of things or something multifactorial... high stress (high cortisol) with slight caloric surplus could explain your weight gain; as could increase in muscle mass during your resistance training; some of this weight may also be attributed to water retention & increased carbohydrate consumption & glycogen storage.
It could also be attributed to hypothyroidism if you have other symptoms, as well as a whole host of other syndromes and diseases and physiological states (pregnancy).
If you are truly concerned, and truly cannot figure out what is going on... I suggest you go to see your doctor, get some bloods done and get your BMI, body composition (skinfold calipers) and general health checked.
If you are not really concerned, you could use a food tracker in the coming weeks/months (myfitnesspal is a good one) and exercise like you normally would and see what your weight does.

Tysm for your advice! Tbh thinking about the last few months, I think you're right it's probs multifactorial. I don't have any other symptoms so I doubt it's anything more worrying. It's helpful to have some outside advice tho, thank you!