Me [18M] and my girlfriend [18F]

Hello everyone, This is my first serious relationship, and it's long-distance. We see each other for about 10 days each month, and we've been together for nearly six months now. I tend to overthink things, especially since after the first couple of months, she started becoming distant for no apparent reason. I understand it's just part of her personality, and she acknowledges it too, often apologizing for her behavior after her phases of being distant, which usually last 1-2 weeks. After those periods, she acts normally for a week, but then the cycle repeats. I refer to it as being distant, but I sometimes wonder if I’m overreacting. There are times when our texting decreases, and she can come off as less affectionate, which leads to fewer calls. Despite this, we’re still on good terms. I’m seeking advice on how to manage my overthinking, as I know it can be frustrating for her, and often she ends up getting annoyed with me. Thank you to everyone who takes the time to respond! Have a great day!