Havent made bowel movement in 3 weeks can it be part of my depo shot?

It's not impossible that Depo ingredients could be affecting your bowel. Hormones can do that.
I'd try to get your bowel moving daily, first, to see if you can sort it out, before assuming it's the Depo.
Senna is good at getting things moving gently. You can buy tablets if you don't want to prepare the leaf yourself.
If you aren't drinking enough water each day, then your bowel will retain stools. It takes a good amount of water each day to keep things moving properly.
Some medications can cause constipation, such as codeine. It's worth checking side effects of any other drugs you are on.
Getting enough fibre into your diet can help with constipation.
Dates & figs can be good for getting things moving. Aloe Vera juice is great for helping, too. Very effective.
While your bowel is retaining stools, it is also retaining all the toxins that your body needs to get rid of, so it's v important to get it moving daily.
Colonic Irrigation/hydrotherapy is very helpful. I've had many of those & felt much better afterwards. Go for a practitioner that uses a machine to do it, rather than a water supply, gravity fed. Much more effective.