I am a 62 yr old male w/ oic (on/ off for 2 weeks) after starting oxycodone 15mg /day. is it ok to combine senna-s, wheat dextrin, and miralax?

Generally, yes: But I usually recommend doing things stepwise rather than all at once. Wheat dextrin is basically a bulk agent, and those are NOT recommended in OIC. Miralax alone should work, just need to escalate dose. Start with one ounce three times daily, and double it until there are results. The newer agents that specifically antagonize opioids gut action, usually without systemic effects, also help.