Recently started weight training. nothing extreme, just legs and abs. ive been very very tired since. is this normal or am i doing something wrong?

This is normal: When you lift weights, you expose your active muscles to repetitive stress loads that increase their size over time. However, the amount of effort required during your workout can also trigger a form of temporary soreness called delayed onset muscle soreness, or DOMS. When DOMS is present, your muscles rest, rebuild and grow larger.