I wanted to make drawing animations (like whiteboard etc...) everywhere I could find it costs money, and doing it on adobe after effects is difficult for me. Have any suggestions (for simple medical illustrations).
Your selection of softawre might change dependent on what kind of animation you want to make, its duration, etc.
You could try creating animations by designing and building sequences of .gifs, then editing them together for something longer. There are a lot of free gif-making programs. Photoshop, a non-animation program you may have access to, also does an excellent job of this.
Inkscape, an open-source drawing package has a plug-in for animating its .svg files: https://thebusiness.itch.io/svg-animation-assistant, but I’ve not tried this.
If you were going for a rough-cut, pre-viz feel, you could use almost any presentation ware program such as Powerpoint or Keynote, as suggested by Aryan Shahabian above, and rendering out .mp4 or .mov files.
If you wanted something more ambitious and three-dimensional you could do a lot worse than Blender.