Irregular after the shot

So for years I took birth control pills, and I switched to the shot because every once in a while I would forget the pill, and intercourse was more regular at this time. So, after taking the shot every three months for only two shots total, I was gaining a lot of weight and decided to stop taking it.

After stopping the shot, I didn't get any periods again for three years. I have not taken any other form of birth control since then, and the only time I got a period was when I was on clomid for two consecutive months in late feb and early April.

After finishing the clomid, no period again for months until two days ago. I had very light spotting which ended yesterday (so a duration of two days). Before the shot, I got a normal period every month of about a 5 day duration.

I've been trying to get a regular cycle back so that I can try getting pregnant again. Has anyone had any similar issues? Any idea what might be going on? Any possibility it could be implantation bleeding? Any tips or tricks? TIA