Worried about baby's development

So my son has always been kinda slow with development. He didn't roll over til 6 months and will only roll from back to tummy and only one direction. He doesn't roll at all now because he's crawling which he didn't do until almost 8 months. But once he started crawling he like caught up i guess. All in the same week he pulled up and stood by himself with one hand on the couch to keep balance and started doing other things he should've done around 6 months. Now he refuses to stand and doesn't do anything he should be able to do. Has never mimicked, doesn't wave, and he use to say mama and Dada and baba MD babi. Now just says baba and mama when he's mad. And the most serious I think is he hasn't gained weight or grown length wise since he was 5 months old. He just doesn't look like he's 8 1/2 months old. Am I overreacting?