About google adsense you can use more than 3 units but it must be of diferent type-
-content, link units , search https://support.google.com/adsense/answer/1346295?hl=enEnsuring proper ad placement
Ad limit per page
Currently, on each page AdSense publishers
may place:
Up to three AdSense for content units
Up to three link units
Up to two search boxes Publishers may not place more than one "large" ad unit per page. We define a
ad unit as any unit similar in size to our 300x600 format. For example, this would include our
300x1050 and 970x250 formats, our 750x200 and 580x400 regional formats, and any other custom sized
ad with comparable dimensions.
However, keep in mind that placing the maximum number of allowed ad
units on a page might result in it looking cluttered. Read our optimization guidelines for tips on
where to place your ads. For best practices on custom sized ad units, review our custom-sized ad units page
.
Mobile implementations: The above ad limits also apply to mobile sites. In addition, two or more AdSense
ads may not appear on the screen at the same time on a mobile site. Publishers with sites using responsive
website should consider that ad units may shift into non-compliant positions as the site scales across
different devices.
https://support.google.com/adsense/answer/1346295?hl=en