Why do I have periods like 1-2 weeks when I can't stop thinking about my ex and I am depressed, and why am I totally fine after that for a few days(then it starts again)?

When you break up with someone you have this period where you try to find out why the relationship had to end, and its something you can't accept. After that period, your subconscious stores that unsolved feeling and you feel better. But as long as you don't get over with that feeling for real, your past will revive at times in your mind and haunt you. A relationship is not in your hands only, its in the hands of the other person too, you have to know that sometimes the answer will not be as clears as we demand and thats why you have to take care of yourself, thinking about you first, not why it ended. Be confident about yourself, you're special!

Sometimes we think of only the good that occurred in a bad relationship, then reality hits. We realize that we deserve better and then our feelings change because we are human, as long as we have feelings for someone our feelings will fluctuate.

different emotion takes place at different time, most of the time we're affected by daily situation.

It's all a part of the process of moving on with life. What you describe is actually very common, especially in situations where the breakup is still pretty recent. When you part ways with someone you care for, it's never easy. You'll have moments were you feel like everything is getting better and sometimes all it will take is one reminder to send you reeling again. It's important to remember that this is a process, and the more you continue to push forward, the easier it gets and the less you will find yourself thinking about them.

I don't know how long it has since the breakup, but sometimes ex's come into our minds because of memories (physical memories: pictures, songs, etc) and when that happens, you attach to your mind and ask more questions to yourself about it, but when you get into those periods of "oblivion", it is because you spend your time doing more things, things that you enjoy. Also notice that it is not bad to remember, getting over is not a synonym of forgetting, it means you have forgiven and you don't let it hurt you anymore.

I often find myself thinking of my ex in times of boredom and loneliness. When my days are busy, and I’ve had lots of tasks to do, I don’t reflect on the past and think of my ex. I think overthinking can happen for extended periods of time causing thoughts like this if an ex. However, by occupying your time and using your brain for other stuff makes you think of a different topic. When I think of an ex, I’ll find things to do like clean or read. These often make me realize that I’m bored/overthinking not genuinely feeling this way.

It is inevitable that there are going to be times when exes pop up in your head. They probably meant a lot at one point and that never just goes away. It's a hard feeling, but it'll ease off soon. Break ups can be hard, whatever the part you played and therefre it is always going to be something swimming around in your head.

Its all about fellings . when we are attached to some one closely we get a habbit of there love and care . When we dont get it we fell like alone . We need some one to fill that place of your ex in ur heart.

Thinking about your ex might be causing stress and thus the hormonal changes in the body causes your cycle to alter.

Well, being stressed out can tend to change our menstrual cycles a lot. Just try to reduce your stress. Stay away from the things that are stressing you out the most and if you feel like you may still have feelings for your ex, try to talk to him/her about these feelings or talk to someone about it and maybe then you won't be so stressed out.

when a relationship breaks down we go through a period of mourning. This is something very hard to deal with, it's a chapter that's ended in your life.. You need time to adjust! Let yourself grieve and let yourself release the pain. One day you will wake up and realize you have moved on and you won't feel the same about him anymore.

It sounds like you have some unresolved issues regarding how you feel about your ex. Rather than actually confront your feelings, you may be trying to repress them, which allows for them to resurface periodically. Consider seeking professional help if you find such thoughts consuming.